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diff --git a/dom/html/HTMLImageElement.h b/dom/html/HTMLImageElement.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_HTMLImageElement_h
+#define mozilla_dom_HTMLImageElement_h
+
+#include "mozilla/Attributes.h"
+#include "nsGenericHTMLElement.h"
+#include "nsImageLoadingContent.h"
+#include "Units.h"
+#include "nsCycleCollectionParticipant.h"
+
+namespace mozilla {
+class EventChainPreVisitor;
+namespace dom {
+
+class ImageLoadTask;
+
+class ResponsiveImageSelector;
+class HTMLImageElement final : public nsGenericHTMLElement,
+                               public nsImageLoadingContent {
+  friend class HTMLSourceElement;
+  friend class HTMLPictureElement;
+  friend class ImageLoadTask;
+
+ public:
+  explicit HTMLImageElement(
+      already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo);
+
+  static already_AddRefed<HTMLImageElement> Image(
+      const GlobalObject& aGlobal, const Optional<uint32_t>& aWidth,
+      const Optional<uint32_t>& aHeight, ErrorResult& aError);
+
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(HTMLImageElement,
+                                           nsGenericHTMLElement)
+
+  // nsISupports
+  NS_DECL_ISUPPORTS_INHERITED
+
+  virtual bool Draggable() const override;
+
+  ResponsiveImageSelector* GetResponsiveImageSelector() {
+    return mResponsiveSelector.get();
+  }
+
+  // Element
+  virtual bool IsInteractiveHTMLContent() const override;
+
+  // EventTarget
+  virtual void AsyncEventRunning(AsyncEventDispatcher* aEvent) override;
+
+  NS_IMPL_FROMNODE_HTML_WITH_TAG(HTMLImageElement, img)
+
+  // override from nsImageLoadingContent
+  CORSMode GetCORSMode() override;
+
+  // nsIContent
+  virtual bool ParseAttribute(int32_t aNamespaceID, nsAtom* aAttribute,
+                              const nsAString& aValue,
+                              nsIPrincipal* aMaybeScriptedPrincipal,
+                              nsAttrValue& aResult) override;
+  virtual nsChangeHint GetAttributeChangeHint(const nsAtom* aAttribute,
+                                              int32_t aModType) const override;
+  NS_IMETHOD_(bool) IsAttributeMapped(const nsAtom* aAttribute) const override;
+  virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction()
+      const override;
+
+  void GetEventTargetParent(EventChainPreVisitor& aVisitor) override;
+  nsINode* GetScopeChainParent() const override;
+
+  bool IsHTMLFocusable(bool aWithMouse, bool* aIsFocusable,
+                       int32_t* aTabIndex) override;
+
+  virtual nsresult BindToTree(BindContext&, nsINode& aParent) override;
+  virtual void UnbindFromTree(bool aNullParent) override;
+
+  virtual ElementState IntrinsicState() const override;
+  virtual nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override;
+
+  virtual void NodeInfoChanged(Document* aOldDoc) override;
+
+  nsresult CopyInnerTo(HTMLImageElement* aDest);
+
+  void MaybeLoadImage(bool aAlwaysForceLoad);
+
+  bool IsMap() { return GetBoolAttr(nsGkAtoms::ismap); }
+  void SetIsMap(bool aIsMap, ErrorResult& aError) {
+    SetHTMLBoolAttr(nsGkAtoms::ismap, aIsMap, aError);
+  }
+  MOZ_CAN_RUN_SCRIPT uint32_t Width();
+  void SetWidth(uint32_t aWidth, ErrorResult& aError) {
+    SetUnsignedIntAttr(nsGkAtoms::width, aWidth, 0, aError);
+  }
+  MOZ_CAN_RUN_SCRIPT uint32_t Height();
+  void SetHeight(uint32_t aHeight, ErrorResult& aError) {
+    SetUnsignedIntAttr(nsGkAtoms::height, aHeight, 0, aError);
+  }
+
+  nsIntSize NaturalSize();
+  uint32_t NaturalHeight() { return NaturalSize().height; }
+  uint32_t NaturalWidth() { return NaturalSize().width; }
+
+  bool Complete();
+  uint32_t Hspace() {
+    return GetDimensionAttrAsUnsignedInt(nsGkAtoms::hspace, 0);
+  }
+  void SetHspace(uint32_t aHspace, ErrorResult& aError) {
+    SetUnsignedIntAttr(nsGkAtoms::hspace, aHspace, 0, aError);
+  }
+  uint32_t Vspace() {
+    return GetDimensionAttrAsUnsignedInt(nsGkAtoms::vspace, 0);
+  }
+  void SetVspace(uint32_t aVspace, ErrorResult& aError) {
+    SetUnsignedIntAttr(nsGkAtoms::vspace, aVspace, 0, aError);
+  }
+
+  void GetAlt(nsAString& aAlt) { GetHTMLAttr(nsGkAtoms::alt, aAlt); }
+  void SetAlt(const nsAString& aAlt, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::alt, aAlt, aError);
+  }
+  void GetSrc(nsAString& aSrc) { GetURIAttr(nsGkAtoms::src, nullptr, aSrc); }
+  void SetSrc(const nsAString& aSrc, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::src, aSrc, aError);
+  }
+  void SetSrc(const nsAString& aSrc, nsIPrincipal* aTriggeringPrincipal,
+              ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::src, aSrc, aTriggeringPrincipal, aError);
+  }
+  void GetSrcset(nsAString& aSrcset) {
+    GetHTMLAttr(nsGkAtoms::srcset, aSrcset);
+  }
+  void SetSrcset(const nsAString& aSrcset, nsIPrincipal* aTriggeringPrincipal,
+                 ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::srcset, aSrcset, aTriggeringPrincipal, aError);
+  }
+  void GetCrossOrigin(nsAString& aResult) {
+    // Null for both missing and invalid defaults is ok, since we
+    // always parse to an enum value, so we don't need an invalid
+    // default, and we _want_ the missing default to be null.
+    GetEnumAttr(nsGkAtoms::crossorigin, nullptr, aResult);
+  }
+  void SetCrossOrigin(const nsAString& aCrossOrigin, ErrorResult& aError) {
+    SetOrRemoveNullableStringAttr(nsGkAtoms::crossorigin, aCrossOrigin, aError);
+  }
+  void GetUseMap(nsAString& aUseMap) {
+    GetHTMLAttr(nsGkAtoms::usemap, aUseMap);
+  }
+  void SetUseMap(const nsAString& aUseMap, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::usemap, aUseMap, aError);
+  }
+  void GetName(nsAString& aName) { GetHTMLAttr(nsGkAtoms::name, aName); }
+  void SetName(const nsAString& aName, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::name, aName, aError);
+  }
+  void GetAlign(nsAString& aAlign) { GetHTMLAttr(nsGkAtoms::align, aAlign); }
+  void SetAlign(const nsAString& aAlign, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::align, aAlign, aError);
+  }
+  void GetLongDesc(nsAString& aLongDesc) {
+    GetURIAttr(nsGkAtoms::longdesc, nullptr, aLongDesc);
+  }
+  void SetLongDesc(const nsAString& aLongDesc, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::longdesc, aLongDesc, aError);
+  }
+  void GetSizes(nsAString& aSizes) { GetHTMLAttr(nsGkAtoms::sizes, aSizes); }
+  void SetSizes(const nsAString& aSizes, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::sizes, aSizes, aError);
+  }
+  void GetCurrentSrc(nsAString& aValue);
+  void GetBorder(nsAString& aBorder) {
+    GetHTMLAttr(nsGkAtoms::border, aBorder);
+  }
+  void SetBorder(const nsAString& aBorder, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::border, aBorder, aError);
+  }
+  void SetReferrerPolicy(const nsAString& aReferrer, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::referrerpolicy, aReferrer, aError);
+  }
+  void GetReferrerPolicy(nsAString& aReferrer) {
+    GetEnumAttr(nsGkAtoms::referrerpolicy, "", aReferrer);
+  }
+  void SetDecoding(const nsAString& aDecoding, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::decoding, aDecoding, aError);
+  }
+  void GetDecoding(nsAString& aValue);
+
+  enum class Loading : uint8_t {
+    Eager,
+    Lazy,
+  };
+
+  void SetLoading(const nsAString& aLoading, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::loading, aLoading, aError);
+  }
+  void GetLoading(nsAString&) const;
+
+  bool IsAwaitingLoadOrLazyLoading() const {
+    return mLazyLoading || mPendingImageLoadTask;
+  }
+
+  bool IsLazyLoading() const { return mLazyLoading; }
+
+  Loading LoadingState() const;
+
+  already_AddRefed<Promise> Decode(ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT int32_t X();
+  MOZ_CAN_RUN_SCRIPT int32_t Y();
+  void GetLowsrc(nsAString& aLowsrc) {
+    GetURIAttr(nsGkAtoms::lowsrc, nullptr, aLowsrc);
+  }
+  void SetLowsrc(const nsAString& aLowsrc, ErrorResult& aError) {
+    SetHTMLAttr(nsGkAtoms::lowsrc, aLowsrc, aError);
+  }
+
+#ifdef DEBUG
+  HTMLFormElement* GetForm() const;
+#endif
+  void SetForm(HTMLFormElement* aForm);
+  void ClearForm(bool aRemoveFromForm);
+
+  virtual void DestroyContent() override;
+
+  void MediaFeatureValuesChanged();
+
+  /**
+   * Given a hypothetical <img> or <source> tag with the given parameters,
+   * return what URI we would attempt to use, if any.  Used by the preloader to
+   * resolve sources prior to DOM creation.
+   *
+   * @param aDocument The document this image would be for, for referencing
+   *        viewport width and DPI/zoom
+   * @param aIsSourceTag If these parameters are for a <source> tag (as in a
+   *        <picture>) rather than an <img> tag. Note that some attrs are unused
+   *        when this is true an vice versa
+   * @param aSrcAttr [ignored if aIsSourceTag] The src attr for this image.
+   * @param aSrcsetAttr The srcset attr for this image/source
+   * @param aSizesAttr The sizes attr for this image/source
+   * @param aTypeAttr [ignored if !aIsSourceTag] The type attr for this source.
+   *                  Should be a void string to differentiate no type attribute
+   *                  from an empty one.
+   * @param aMediaAttr [ignored if !aIsSourceTag] The media attr for this
+   *                   source.  Should be a void string to differentiate no
+   *                   media attribute from an empty one.
+   * @param aResult A reference to store the resulting URL spec in if we
+   *                selected a source.  This value is not guaranteed to parse to
+   *                a valid URL, merely the URL that the tag would attempt to
+   *                resolve and load (which may be the empty string).  This
+   *                parameter is not modified if return value is false.
+   * @return True if we were able to select a final source, false if further
+   *         sources would be considered.  It follows that this always returns
+   *         true if !aIsSourceTag.
+   *
+   * Note that the return value may be true with an empty string as the result,
+   * which implies that the parameters provided describe a tag that would select
+   * no source.  This is distinct from a return of false which implies that
+   * further <source> or <img> tags would be considered.
+   */
+  static bool SelectSourceForTagWithAttrs(
+      Document* aDocument, bool aIsSourceTag, const nsAString& aSrcAttr,
+      const nsAString& aSrcsetAttr, const nsAString& aSizesAttr,
+      const nsAString& aTypeAttr, const nsAString& aMediaAttr,
+      nsAString& aResult);
+
+  enum class FromIntersectionObserver : bool { No, Yes };
+  enum class StartLoading : bool { No, Yes };
+  void StopLazyLoading(StartLoading);
+
+  // This is used when restyling, for retrieving the extra style from the source
+  // element.
+  const nsMappedAttributes* GetMappedAttributesFromSource() const;
+
+ protected:
+  virtual ~HTMLImageElement();
+
+  // Update the responsive source synchronously and queues a task to run
+  // LoadSelectedImage pending stable state.
+  //
+  // Pending Bug 1076583 this is only used by the responsive image
+  // algorithm (InResponsiveMode()) -- synchronous actions when just
+  // using img.src will bypass this, and update source and kick off
+  // image load synchronously.
+  void UpdateSourceSyncAndQueueImageTask(
+      bool aAlwaysLoad, const HTMLSourceElement* aSkippedSource = nullptr);
+
+  // True if we have a srcset attribute or a <picture> parent, regardless of if
+  // any valid responsive sources were parsed from either.
+  bool HaveSrcsetOrInPicture();
+
+  // True if we are using the newer image loading algorithm. This will be the
+  // only mode after Bug 1076583
+  bool InResponsiveMode();
+
+  // True if the given URL equals the last URL that was loaded by this element.
+  bool SelectedSourceMatchesLast(nsIURI* aSelectedSource);
+
+  // Load the current mResponsiveSelector (responsive mode) or src attr image.
+  // Note: This doesn't run the full selection for the responsive selector.
+  nsresult LoadSelectedImage(bool aForce, bool aNotify, bool aAlwaysLoad);
+
+  // True if this string represents a type we would support on <source type>
+  static bool SupportedPictureSourceType(const nsAString& aType);
+
+  // Update/create/destroy mResponsiveSelector
+  void PictureSourceSrcsetChanged(nsIContent* aSourceNode,
+                                  const nsAString& aNewValue, bool aNotify);
+  void PictureSourceSizesChanged(nsIContent* aSourceNode,
+                                 const nsAString& aNewValue, bool aNotify);
+  // As we re-run the source selection on these mutations regardless,
+  // we don't actually care which changed or to what
+  void PictureSourceMediaOrTypeChanged(nsIContent* aSourceNode, bool aNotify);
+
+  // This is called when we update "width" or "height" attribute of source
+  // element.
+  void PictureSourceDimensionChanged(HTMLSourceElement* aSourceNode,
+                                     bool aNotify);
+
+  void PictureSourceAdded(HTMLSourceElement* aSourceNode = nullptr);
+  // This should be called prior to the unbind, such that nextsibling works
+  void PictureSourceRemoved(HTMLSourceElement* aSourceNode = nullptr);
+
+  // Re-evaluates all source nodes (picture <source>,<img>) and finds
+  // the best source set for mResponsiveSelector. If a better source
+  // is found, creates a new selector and feeds the source to it. If
+  // the current ResponsiveSelector is not changed, runs
+  // SelectImage(true) to re-evaluate its candidates.
+  //
+  // Because keeping the existing selector is the common case (and we
+  // often do no-op reselections), this does not re-parse values for
+  // the existing mResponsiveSelector, meaning you need to update its
+  // parameters as appropriate before calling (or null it out to force
+  // recreation)
+  //
+  // if |aSkippedSource| is non-null, we will skip it when running the
+  // algorithm. This is used when we need to update the source when we are
+  // removing the source element.
+  //
+  // Returns true if the source has changed, and false otherwise.
+  bool UpdateResponsiveSource(
+      const HTMLSourceElement* aSkippedSource = nullptr);
+
+  // Given a <source> node that is a previous sibling *or* ourselves, try to
+  // create a ResponsiveSelector.
+
+  // If the node's srcset/sizes make for an invalid selector, returns
+  // nullptr. This does not guarantee the resulting selector matches an image,
+  // only that it is valid.
+  already_AddRefed<ResponsiveImageSelector> TryCreateResponsiveSelector(
+      Element* aSourceElement);
+
+  MOZ_CAN_RUN_SCRIPT CSSIntPoint GetXY();
+  virtual JSObject* WrapNode(JSContext* aCx,
+                             JS::Handle<JSObject*> aGivenProto) override;
+  void UpdateFormOwner();
+
+  void BeforeSetAttr(int32_t aNameSpaceID, nsAtom* aName,
+                     const nsAttrValue* aValue, bool aNotify) override;
+
+  void AfterSetAttr(int32_t aNameSpaceID, nsAtom* aName,
+                    const nsAttrValue* aValue, const nsAttrValue* aOldValue,
+                    nsIPrincipal* aMaybeScriptedPrincipal,
+                    bool aNotify) override;
+  void OnAttrSetButNotChanged(int32_t aNamespaceID, nsAtom* aName,
+                              const nsAttrValueOrString& aValue,
+                              bool aNotify) override;
+
+  // Override for nsImageLoadingContent.
+  nsIContent* AsContent() override { return this; }
+
+  // This is a weak reference that this element and the HTMLFormElement
+  // cooperate in maintaining.
+  HTMLFormElement* mForm;
+
+  // Created when we're tracking responsive image state
+  RefPtr<ResponsiveImageSelector> mResponsiveSelector;
+
+ private:
+  bool SourceElementMatches(Element* aSourceElement);
+
+  static void MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
+                                    MappedDeclarations&);
+  /**
+   * This function is called by AfterSetAttr and OnAttrSetButNotChanged.
+   * It will not be called if the value is being unset.
+   *
+   * @param aNamespaceID the namespace of the attr being set
+   * @param aName the localname of the attribute being set
+   * @param aValue the value it's being set to represented as either a string or
+   *        a parsed nsAttrValue.
+   * @param aOldValue the value previously set. Will be null if no value was
+   *        previously set. This value should only be used when
+   *        aValueMaybeChanged is true; when aValueMaybeChanged is false,
+   *        aOldValue should be considered unreliable.
+   * @param aNotify Whether we plan to notify document observers.
+   */
+  void AfterMaybeChangeAttr(int32_t aNamespaceID, nsAtom* aName,
+                            const nsAttrValueOrString& aValue,
+                            const nsAttrValue* aOldValue,
+                            nsIPrincipal* aMaybeScriptedPrincipal,
+                            bool aNotify);
+
+  bool ShouldLoadImage() const;
+
+  // Set this image as a lazy load image due to loading="lazy".
+  void SetLazyLoading();
+
+  void StartLoadingIfNeeded();
+
+  bool IsInPicture() const {
+    return GetParentElement() &&
+           GetParentElement()->IsHTMLElement(nsGkAtoms::picture);
+  }
+
+  void InvalidateAttributeMapping();
+
+  void SetResponsiveSelector(RefPtr<ResponsiveImageSelector>&& aSource);
+  void SetDensity(double aDensity);
+
+  // Queue an image load task (via microtask).
+  void QueueImageLoadTask(bool aAlwaysLoad);
+
+  bool mInDocResponsiveContent;
+
+  RefPtr<ImageLoadTask> mPendingImageLoadTask;
+  nsCOMPtr<nsIPrincipal> mSrcTriggeringPrincipal;
+  nsCOMPtr<nsIPrincipal> mSrcsetTriggeringPrincipal;
+
+  // Last URL that was attempted to load by this element.
+  nsCOMPtr<nsIURI> mLastSelectedSource;
+  // Last pixel density that was selected.
+  double mCurrentDensity;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_HTMLImageElement_h */