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diff --git a/image/ISurfaceProvider.h b/image/ISurfaceProvider.h
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+++ b/image/ISurfaceProvider.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/**
+ * An interface for objects which can either store a surface or dynamically
+ * generate one, and various implementations.
+ */
+
+#ifndef mozilla_image_ISurfaceProvider_h
+#define mozilla_image_ISurfaceProvider_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/image/WebRenderImageProvider.h"
+
+#include "imgFrame.h"
+#include "SurfaceCache.h"
+
+namespace mozilla {
+namespace image {
+
+class CachedSurface;
+class DrawableSurface;
+
+/**
+ * An interface for objects which can either store a surface or dynamically
+ * generate one.
+ */
+class ISurfaceProvider : public WebRenderImageProvider {
+ public:
+  // Subclasses may or may not be XPCOM classes, so we just require that they
+  // implement AddRef and Release.
+  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+  /// @return key data used for identifying which image this ISurfaceProvider is
+  /// associated with in the surface cache.
+  ImageKey GetImageKey() const { return mImageKey; }
+
+  /// @return key data used to uniquely identify this ISurfaceProvider's cache
+  /// entry in the surface cache.
+  const SurfaceKey& GetSurfaceKey() const { return mSurfaceKey; }
+
+  /// @return a drawable reference to a surface.
+  DrawableSurface Surface();
+
+  /// @return true if DrawableRef() will return a completely decoded surface.
+  virtual bool IsFinished() const = 0;
+
+  /// @return true if the underlying decoder is currently fully decoded. For
+  /// animated images, this means that at least every frame has been decoded
+  /// at least once. It does not guarantee that all of the frames are present,
+  /// as the surface provider has the option to discard as it deems necessary.
+  virtual bool IsFullyDecoded() const { return IsFinished(); }
+
+  /// @return the number of bytes of memory this ISurfaceProvider is expected to
+  /// require. Optimizations may result in lower real memory usage. Trivial
+  /// overhead is ignored. Because this value is used in bookkeeping, it's
+  /// important that it be constant over the lifetime of this object.
+  virtual size_t LogicalSizeInBytes() const = 0;
+
+  typedef imgFrame::AddSizeOfCbData AddSizeOfCbData;
+  typedef imgFrame::AddSizeOfCb AddSizeOfCb;
+
+  /// @return the actual number of bytes of memory this ISurfaceProvider is
+  /// using. May vary over the lifetime of the ISurfaceProvider. The default
+  /// implementation is appropriate for static ISurfaceProviders.
+  virtual void AddSizeOfExcludingThis(MallocSizeOf aMallocSizeOf,
+                                      const AddSizeOfCb& aCallback) {
+    DrawableFrameRef ref = DrawableRef(/* aFrame = */ 0);
+    if (!ref) {
+      return;
+    }
+
+    ref->AddSizeOfExcludingThis(aMallocSizeOf, aCallback);
+  }
+
+  virtual void Reset() {}
+  virtual void Advance(size_t aFrame) {}
+  virtual bool MayAdvance() const { return false; }
+  virtual void MarkMayAdvance() {}
+
+  /// @return the availability state of this ISurfaceProvider, which indicates
+  /// whether DrawableRef() could successfully return a surface. Should only be
+  /// called from SurfaceCache code as it relies on SurfaceCache for
+  /// synchronization.
+  AvailabilityState& Availability() { return mAvailability; }
+  const AvailabilityState& Availability() const { return mAvailability; }
+
+ protected:
+  ISurfaceProvider(const ImageKey aImageKey, const SurfaceKey& aSurfaceKey,
+                   AvailabilityState aAvailability)
+      : WebRenderImageProvider(aImageKey),
+        mImageKey(aImageKey),
+        mSurfaceKey(aSurfaceKey),
+        mAvailability(aAvailability) {
+    MOZ_ASSERT(aImageKey, "Must have a valid image key");
+  }
+
+  virtual ~ISurfaceProvider() {}
+
+  /// @return an eagerly computed drawable reference to a surface. For
+  /// dynamically generated animation surfaces, @aFrame specifies the 0-based
+  /// index of the desired frame.
+  virtual DrawableFrameRef DrawableRef(size_t aFrame) = 0;
+
+  /// @return an imgFrame at the 0-based index of the desired frame, as
+  /// specified by @aFrame. Only applies for animated images.
+  virtual already_AddRefed<imgFrame> GetFrame(size_t aFrame) {
+    MOZ_ASSERT_UNREACHABLE("Surface provider does not support direct access!");
+    return nullptr;
+  }
+
+  /// @return true if this ISurfaceProvider is locked. (@see SetLocked())
+  /// Should only be called from SurfaceCache code as it relies on SurfaceCache
+  /// for synchronization.
+  virtual bool IsLocked() const = 0;
+
+  /// If @aLocked is true, hint that this ISurfaceProvider is in use and it
+  /// should avoid releasing its resources. Should only be called from
+  /// SurfaceCache code as it relies on SurfaceCache for synchronization.
+  virtual void SetLocked(bool aLocked) = 0;
+
+ private:
+  friend class CachedSurface;
+  friend class DrawableSurface;
+
+  const ImageKey mImageKey;
+  const SurfaceKey mSurfaceKey;
+  AvailabilityState mAvailability;
+};
+
+/**
+ * A reference to a surface (stored in an imgFrame) that holds the surface in
+ * memory, guaranteeing that it can be drawn. If you have a DrawableSurface
+ * |surf| and |if (surf)| returns true, then calls to |surf->Draw()| and
+ * |surf->GetSourceSurface()| are guaranteed to succeed.
+ *
+ * Note that the surface may be computed lazily, so a DrawableSurface should not
+ * be dereferenced (i.e., operator->() should not be called) until you're
+ * sure that you want to draw it.
+ */
+class MOZ_STACK_CLASS DrawableSurface final {
+ public:
+  DrawableSurface() : mHaveSurface(false) {}
+
+  explicit DrawableSurface(NotNull<ISurfaceProvider*> aProvider)
+      : mProvider(aProvider), mHaveSurface(true) {}
+
+  DrawableSurface(DrawableSurface&& aOther)
+      : mDrawableRef(std::move(aOther.mDrawableRef)),
+        mProvider(std::move(aOther.mProvider)),
+        mHaveSurface(aOther.mHaveSurface) {
+    aOther.mHaveSurface = false;
+  }
+
+  DrawableSurface& operator=(DrawableSurface&& aOther) {
+    MOZ_ASSERT(this != &aOther, "Self-moves are prohibited");
+    mDrawableRef = std::move(aOther.mDrawableRef);
+    mProvider = std::move(aOther.mProvider);
+    mHaveSurface = aOther.mHaveSurface;
+    aOther.mHaveSurface = false;
+    return *this;
+  }
+
+  /**
+   * If this DrawableSurface is dynamically generated from an animation, attempt
+   * to seek to frame @aFrame, where @aFrame is a 0-based index into the frames
+   * of the animation. Otherwise, nothing will blow up at runtime, but we assert
+   * in debug builds, since calling this in an unexpected situation probably
+   * indicates a bug.
+   *
+   * @return a successful result if we could obtain frame @aFrame. Note that
+   * |mHaveSurface| being true means that we're guaranteed to have *some* frame,
+   * so the caller can dereference this DrawableSurface even if Seek() fails,
+   * but while nothing will blow up, the frame won't be the one they expect.
+   */
+  nsresult Seek(size_t aFrame) {
+    MOZ_ASSERT(mHaveSurface, "Trying to seek an empty DrawableSurface?");
+
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to seek a static DrawableSurface?");
+      return NS_ERROR_FAILURE;
+    }
+
+    mDrawableRef = mProvider->DrawableRef(aFrame);
+
+    return mDrawableRef ? NS_OK : NS_ERROR_FAILURE;
+  }
+
+  already_AddRefed<imgFrame> GetFrame(size_t aFrame) {
+    MOZ_ASSERT(mHaveSurface, "Trying to get on an empty DrawableSurface?");
+
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to get on a static DrawableSurface?");
+      return nullptr;
+    }
+
+    return mProvider->GetFrame(aFrame);
+  }
+
+  void Reset() {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to reset a static DrawableSurface?");
+      return;
+    }
+
+    mProvider->Reset();
+  }
+
+  void Advance(size_t aFrame) {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to advance a static DrawableSurface?");
+      return;
+    }
+
+    mProvider->Advance(aFrame);
+  }
+
+  bool MayAdvance() const {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to advance a static DrawableSurface?");
+      return false;
+    }
+
+    return mProvider->MayAdvance();
+  }
+
+  void MarkMayAdvance() {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE("Trying to advance a static DrawableSurface?");
+      return;
+    }
+
+    mProvider->MarkMayAdvance();
+  }
+
+  bool IsFullyDecoded() const {
+    if (!mProvider) {
+      MOZ_ASSERT_UNREACHABLE(
+          "Trying to check decoding state of a static DrawableSurface?");
+      return false;
+    }
+
+    return mProvider->IsFullyDecoded();
+  }
+
+  void TakeProvider(WebRenderImageProvider** aOutProvider) {
+    mProvider.forget(aOutProvider);
+  }
+
+  explicit operator bool() const { return mHaveSurface; }
+  imgFrame* operator->() { return DrawableRef().get(); }
+
+ private:
+  DrawableSurface(const DrawableSurface& aOther) = delete;
+  DrawableSurface& operator=(const DrawableSurface& aOther) = delete;
+
+  DrawableFrameRef& DrawableRef() {
+    MOZ_ASSERT(mHaveSurface);
+
+    // If we weren't created with a DrawableFrameRef directly, we should've been
+    // created with an ISurfaceProvider which can give us one. Note that if
+    // Seek() has been called, we'll already have a DrawableFrameRef, so we
+    // won't need to get one here.
+    if (!mDrawableRef) {
+      MOZ_ASSERT(mProvider);
+      mDrawableRef = mProvider->DrawableRef(/* aFrame = */ 0);
+    }
+
+    MOZ_ASSERT(mDrawableRef);
+    return mDrawableRef;
+  }
+
+  DrawableFrameRef mDrawableRef;
+  RefPtr<ISurfaceProvider> mProvider;
+  bool mHaveSurface;
+};
+
+// Surface() is implemented here so that DrawableSurface's definition is
+// visible.
+inline DrawableSurface ISurfaceProvider::Surface() {
+  return DrawableSurface(WrapNotNull(this));
+}
+
+/**
+ * An ISurfaceProvider that stores a single surface.
+ */
+class SimpleSurfaceProvider final : public ISurfaceProvider {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SimpleSurfaceProvider, override)
+
+  SimpleSurfaceProvider(const ImageKey aImageKey, const SurfaceKey& aSurfaceKey,
+                        NotNull<imgFrame*> aSurface)
+      : ISurfaceProvider(aImageKey, aSurfaceKey,
+                         AvailabilityState::StartAvailable()),
+        mSurface(aSurface) {
+    MOZ_ASSERT(aSurfaceKey.Size() == mSurface->GetSize());
+  }
+
+  bool IsFinished() const override { return mSurface->IsFinished(); }
+
+  size_t LogicalSizeInBytes() const override {
+    gfx::IntSize size = mSurface->GetSize();
+    return size.width * size.height * mSurface->GetBytesPerPixel();
+  }
+
+  nsresult UpdateKey(layers::RenderRootStateManager* aManager,
+                     wr::IpcResourceUpdateQueue& aResources,
+                     wr::ImageKey& aKey) override;
+
+ protected:
+  DrawableFrameRef DrawableRef(size_t aFrame) override {
+    MOZ_ASSERT(aFrame == 0,
+               "Requesting an animation frame from a SimpleSurfaceProvider?");
+    return mSurface->DrawableRef();
+  }
+
+  bool IsLocked() const override { return bool(mLockRef); }
+
+  void SetLocked(bool aLocked) override {
+    if (aLocked == IsLocked()) {
+      return;  // Nothing changed.
+    }
+
+    // If we're locked, hold a DrawableFrameRef to |mSurface|, which will keep
+    // any volatile buffer it owns in memory.
+    mLockRef = aLocked ? mSurface->DrawableRef() : DrawableFrameRef();
+  }
+
+ private:
+  virtual ~SimpleSurfaceProvider() {}
+
+  NotNull<RefPtr<imgFrame>> mSurface;
+  DrawableFrameRef mLockRef;
+};
+
+}  // namespace image
+}  // namespace mozilla
+
+#endif  // mozilla_image_ISurfaceProvider_h