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diff --git a/layout/painting/DisplayListClipState.h b/layout/painting/DisplayListClipState.h
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+++ b/layout/painting/DisplayListClipState.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 DISPLAYLISTCLIPSTATE_H_
+#define DISPLAYLISTCLIPSTATE_H_
+
+#include "DisplayItemClip.h"
+#include "DisplayItemClipChain.h"
+
+#include "mozilla/DebugOnly.h"
+
+class nsIFrame;
+class nsIScrollableFrame;
+class nsDisplayListBuilder;
+
+namespace mozilla {
+
+/**
+ * All clip coordinates are in appunits relative to the reference frame
+ * for the display item we're building.
+ */
+class DisplayListClipState {
+ public:
+  DisplayListClipState()
+      : mClipChainContentDescendants(nullptr),
+        mClipChainContainingBlockDescendants(nullptr),
+        mCurrentCombinedClipChain(nullptr),
+        mCurrentCombinedClipChainIsValid(false),
+        mClippedToDisplayPort(false) {}
+
+  void SetClippedToDisplayPort() { mClippedToDisplayPort = true; }
+  bool IsClippedToDisplayPort() const { return mClippedToDisplayPort; }
+
+  /**
+   * Returns intersection of mClipChainContainingBlockDescendants and
+   * mClipChainContentDescendants, allocated on aBuilder's arena.
+   */
+  const DisplayItemClipChain* GetCurrentCombinedClipChain(
+      nsDisplayListBuilder* aBuilder);
+
+  const DisplayItemClipChain* GetClipChainForContainingBlockDescendants()
+      const {
+    return mClipChainContainingBlockDescendants;
+  }
+  const DisplayItemClipChain* GetClipChainForContentDescendants() const {
+    return mClipChainContentDescendants;
+  }
+
+  const ActiveScrolledRoot* GetContentClipASR() const {
+    return mClipChainContentDescendants ? mClipChainContentDescendants->mASR
+                                        : nullptr;
+  }
+
+  class AutoSaveRestore;
+
+  class AutoClipContainingBlockDescendantsToContentBox;
+
+  class AutoClipMultiple;
+
+  enum { ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT = 0x01 };
+
+ private:
+  void Clear() {
+    mClipChainContentDescendants = nullptr;
+    mClipChainContainingBlockDescendants = nullptr;
+    mCurrentCombinedClipChain = nullptr;
+    mCurrentCombinedClipChainIsValid = false;
+    mClippedToDisplayPort = false;
+  }
+
+  void SetClipChainForContainingBlockDescendants(
+      const DisplayItemClipChain* aClipChain) {
+    mClipChainContainingBlockDescendants = aClipChain;
+    InvalidateCurrentCombinedClipChain(aClipChain ? aClipChain->mASR : nullptr);
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(nsDisplayListBuilder* aBuilder,
+                                      const nsRect& aRect,
+                                      const nscoord* aRadii,
+                                      DisplayItemClipChain& aClipChainOnStack);
+
+  void ClipContentDescendants(nsDisplayListBuilder* aBuilder,
+                              const nsRect& aRect, const nscoord* aRadii,
+                              DisplayItemClipChain& aClipChainOnStack);
+  void ClipContentDescendants(nsDisplayListBuilder* aBuilder,
+                              const nsRect& aRect, const nsRect& aRoundedRect,
+                              const nscoord* aRadii,
+                              DisplayItemClipChain& aClipChainOnStack);
+
+  void InvalidateCurrentCombinedClipChain(
+      const ActiveScrolledRoot* aInvalidateUpTo);
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+      DisplayItemClipChain& aClipChainOnStack, uint32_t aFlags);
+
+  /**
+   * All content descendants (i.e. following placeholder frames to their
+   * out-of-flows if necessary) should be clipped by
+   * mClipChainContentDescendants. Null if no clipping applies.
+   */
+  const DisplayItemClipChain* mClipChainContentDescendants;
+  /**
+   * All containing-block descendants (i.e. frame descendants), including
+   * display items for the current frame, should be clipped by
+   * mClipChainContainingBlockDescendants.
+   * Null if no clipping applies.
+   */
+  const DisplayItemClipChain* mClipChainContainingBlockDescendants;
+  /**
+   * The intersection of mClipChainContentDescendants and
+   * mClipChainContainingBlockDescendants.
+   * Allocated in the nsDisplayListBuilder arena. Null if none has been
+   * allocated or both mClipChainContentDescendants and
+   * mClipChainContainingBlockDescendants are null.
+   */
+  const DisplayItemClipChain* mCurrentCombinedClipChain;
+  bool mCurrentCombinedClipChainIsValid;
+  /**
+   * A flag that is used by sticky positioned items to know if the clip applied
+   * to them is just the displayport clip or if there is additional clipping.
+   */
+  bool mClippedToDisplayPort;
+};
+
+/**
+ * A class to automatically save and restore the current clip state. Also
+ * offers methods for modifying the clip state. Only one modification is allowed
+ * to be in scope at a time using one of these objects; multiple modifications
+ * require nested objects. The interface is written this way to prevent
+ * dangling pointers to DisplayItemClips.
+ */
+class DisplayListClipState::AutoSaveRestore {
+ public:
+  explicit AutoSaveRestore(nsDisplayListBuilder* aBuilder);
+  void Restore() {
+    mState = mSavedState;
+#ifdef DEBUG
+    mRestored = true;
+#endif
+  }
+  ~AutoSaveRestore() { Restore(); }
+
+  void Clear() {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    mState.Clear();
+#ifdef DEBUG
+    mClipUsed = false;
+#endif
+  }
+
+  void SetClipChainForContainingBlockDescendants(
+      const DisplayItemClipChain* aClipChain) {
+    mState.SetClipChainForContainingBlockDescendants(aClipChain);
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendants(const nsRect& aRect,
+                                      const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(mBuilder, aRect, aRadii, mClipChain);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect,
+                              const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(mBuilder, aRect, aRadii, mClipChain);
+  }
+
+  void ClipContentDescendants(const nsRect& aRect, const nsRect& aRoundedRect,
+                              const nscoord* aRadii = nullptr) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContentDescendants(mBuilder, aRect, aRoundedRect, aRadii,
+                                  mClipChain);
+  }
+
+  /**
+   * Clips containing-block descendants to the frame's content-box,
+   * taking border-radius into account.
+   * If aFlags contains ASSUME_DRAWING_RESTRICTED_TO_CONTENT_RECT then
+   * we assume display items will not draw outside the content rect, so
+   * clipping is only required if there is a border-radius. This is an
+   * optimization to reduce the amount of clipping required.
+   */
+  void ClipContainingBlockDescendantsToContentBox(
+      nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, uint32_t aFlags = 0) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mClipUsed, "mClip already used");
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame,
+                                                      mClipChain, aFlags);
+  }
+
+  void SetClippedToDisplayPort() { mState.SetClippedToDisplayPort(); }
+  bool IsClippedToDisplayPort() const {
+    return mState.IsClippedToDisplayPort();
+  }
+
+ protected:
+  nsDisplayListBuilder* mBuilder;
+  DisplayListClipState& mState;
+  DisplayListClipState mSavedState;
+  DisplayItemClipChain mClipChain;
+#ifdef DEBUG
+  bool mClipUsed;
+  bool mRestored;
+#endif
+};
+
+class DisplayListClipState::AutoClipContainingBlockDescendantsToContentBox
+    : public AutoSaveRestore {
+ public:
+  AutoClipContainingBlockDescendantsToContentBox(nsDisplayListBuilder* aBuilder,
+                                                 nsIFrame* aFrame,
+                                                 uint32_t aFlags = 0)
+      : AutoSaveRestore(aBuilder) {
+#ifdef DEBUG
+    mClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendantsToContentBox(aBuilder, aFrame,
+                                                      mClipChain, aFlags);
+  }
+};
+
+/**
+ * Do not use this outside of nsIFrame::BuildDisplayListForChild, use
+ * multiple AutoSaveRestores instead. We provide this class just to ensure
+ * BuildDisplayListForChild is as efficient as possible.
+ */
+class DisplayListClipState::AutoClipMultiple : public AutoSaveRestore {
+ public:
+  explicit AutoClipMultiple(nsDisplayListBuilder* aBuilder)
+      : AutoSaveRestore(aBuilder)
+#ifdef DEBUG
+        ,
+        mExtraClipUsed(false)
+#endif
+  {
+  }
+
+  /**
+   * Intersects the given clip rect (with optional aRadii) with the current
+   * mClipContainingBlockDescendants and sets mClipContainingBlockDescendants to
+   * the result, stored in aClipOnStack.
+   */
+  void ClipContainingBlockDescendantsExtra(const nsRect& aRect,
+                                           const nscoord* aRadii) {
+    NS_ASSERTION(!mRestored, "Already restored!");
+    NS_ASSERTION(!mExtraClipUsed, "mExtraClip already used");
+#ifdef DEBUG
+    mExtraClipUsed = true;
+#endif
+    mState.ClipContainingBlockDescendants(mBuilder, aRect, aRadii,
+                                          mExtraClipChain);
+  }
+
+ protected:
+  DisplayItemClipChain mExtraClipChain;
+#ifdef DEBUG
+  bool mExtraClipUsed;
+#endif
+};
+
+}  // namespace mozilla
+
+#endif /* DISPLAYLISTCLIPSTATE_H_ */