Optimize yuv decoding fail check and remove the usage of unwanted variable.

third_party/WebKit/Source/platform/graphics/ImageFrameGenerator.h

 /*
  * Copyright (C) 2012 Google Inc. 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 127 matching lines @@
               SkBitmap::Allocator*,
               ImageDecoder::AlphaOption);
 
   const SkISize full_size_;
 
   // Parameters used to create internal ImageDecoder objects.
   const ColorBehavior decoder_color_behavior_;
 
   const bool is_multi_frame_;
   bool decode_failed_;
-  bool yuv_decoding_failed_;
   size_t frame_count_;
   Vector<bool> has_alpha_;
 
   std::unique_ptr<ImageDecoderFactory> image_decoder_factory_;
 
   // Prevents multiple decode operations on the same data.
   Mutex decode_mutex_;
 
   // Protect concurrent access to m_hasAlpha.
   Mutex alpha_mutex_;
 };
 
 }  // namespace blink
 
 #endif