Add frame count to paint image.

cc/paint/paint_image.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_PAINT_PAINT_IMAGE_H_
 #define CC_PAINT_PAINT_IMAGE_H_
 
 #include "base/logging.h"
 #include "cc/paint/paint_export.h"
 #include "third_party/skia/include/core/SkImage.h"
@@ skipping 17 matching lines @@
 
   // TODO(vmpstr): Work towards removing "UNKNOWN" value.
   enum class AnimationType { UNKNOWN, ANIMATED, VIDEO, STATIC };
 
   // TODO(vmpstr): Work towards removing "UNKNOWN" value.
   enum class CompletionState { UNKNOWN, DONE, PARTIALLY_DONE };
 
   static Id GetNextId();
 
   PaintImage();
+  // - id: stable id for this image; can be generated using GetNextId().
+  // - sk_image: the underlying skia image that this represents.
+  // - animation_type: the animation type of this paint image.
+  // - completion_state: indicates whether the image is completed loading.
+  // - frame_count: the known number of frames in this image. E.g. number of GIF
+  //   frames in an animated GIF.
   explicit PaintImage(Id id,
                       sk_sp<SkImage> sk_image,
                       AnimationType animation_type = AnimationType::STATIC,
-                      CompletionState completion_state = CompletionState::DONE);
+                      CompletionState completion_state = CompletionState::DONE,
+                      size_t frame_count = 0);
   PaintImage(const PaintImage& other);
   PaintImage(PaintImage&& other);
   ~PaintImage();
 
   PaintImage& operator=(const PaintImage& other);
   PaintImage& operator=(PaintImage&& other);
 
   bool operator==(const PaintImage& other) const;
   explicit operator bool() const { return sk_image_; }
 
   Id stable_id() const { return id_; }
   const sk_sp<SkImage>& sk_image() const { return sk_image_; }
   AnimationType animation_type() const { return animation_type_; }
   CompletionState completion_state() const { return completion_state_; }
+  size_t frame_count() const { return frame_count_; }
 
  private:
   Id id_ = kUnknownStableId;
   sk_sp<SkImage> sk_image_;
   AnimationType animation_type_ = AnimationType::UNKNOWN;
   CompletionState completion_state_ = CompletionState::UNKNOWN;
+  // The number of frames known to exist in this image (eg number of GIF frames
+  // loaded). 0 indicates either unknown or only a single frame, both of which
+  // should be treated similarly.
+  size_t frame_count_ = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_PAINT_PAINT_IMAGE_H_