Pull up initFrameBuffer to ImageDecoder.

third_party/WebKit/Source/platform/image-decoders/ImageDecoder.h

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) Research In Motion Limited 2009-2010. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 286 matching lines @@
   size_t clearCacheExceptTwoFrames(size_t, size_t);
   virtual void clearFrameBuffer(size_t frameIndex);
 
   // Decodes the image sufficiently to determine the image size.
   virtual void decodeSize() = 0;
 
   // Decodes the image sufficiently to determine the number of frames and
   // returns that number.
   virtual size_t decodeFrameCount() { return 1; }
 
+  // Called to initialize the frame buffer with the given index, based on the
+  // provided and previous frame's characteristics. Returns true on success. On
+  // failure, this will mark the image as failed. Before calling this method,
+  // the caller must verify that the frame exists.
+  bool initFrameBuffer(size_t);
+
   // Performs any additional setup of the requested frame after it has been
   // initially created, e.g. setting a duration or disposal method.
   virtual void initializeNewFrame(size_t) {}
 
   // Decodes the requested frame.
   virtual void decode(size_t) = 0;
 
   // This method is only required for animated images. It returns a vector with
   // all frame indices that need to be decoded in order to succesfully decode
   // the provided frame.  The indices are returned in reverse order, so the
@@ skipping 34 matching lines @@
   // Some code paths compute the size of the image as "width * height * 4"
   // and return it as a (signed) int.  Avoid overflow.
   static bool sizeCalculationMayOverflow(unsigned width, unsigned height) {
     unsigned long long total_size = static_cast<unsigned long long>(width) *
                                     static_cast<unsigned long long>(height);
     return total_size > ((1 << 29) - 1);
   }
 
   bool m_purgeAggressively;
 
+  // This methods gets called at the end of initFrameBuffer. Subclasses can do
+  // format specific initialization, for e.g. alpha settings, here.
+  virtual void onInitFrameBuffer(size_t){};
+
+  // Called by initFrameBuffer to determine if it can take the bitmap of the
+  // previous frame. This condition is different for GIF and WEBP.
+  virtual bool canReusePreviousFrameBuffer(size_t) const { return false; }
+
   IntSize m_size;
   bool m_sizeAvailable = false;
   bool m_isAllDataReceived = false;
   bool m_failed = false;
   bool m_hasHistogrammedColorSpace = false;
 
   sk_sp<SkColorSpace> m_embeddedColorSpace = nullptr;
   std::unique_ptr<SkColorSpaceXform> m_sourceToOutputDeviceColorTransform;
 };
 
 }  // namespace blink
 
 #endif