Add support for EXT_image_flush_external extension

ui/gl/gl_image_memory.h

 // Copyright 2014 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 UI_GL_GL_IMAGE_MEMORY_H_
 #define UI_GL_GL_IMAGE_MEMORY_H_
 
 #include "ui/gl/gl_image.h"
 
 #include <stddef.h>
@@ skipping 23 matching lines @@
   bool CopyTexSubImage(unsigned target,
                        const gfx::Point& offset,
                        const gfx::Rect& rect) override;
   bool ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
                             int z_order,
                             gfx::OverlayTransform transform,
                             const gfx::Rect& bounds_rect,
                             const gfx::RectF& crop_rect) override;
 
   static unsigned GetInternalFormatForTesting(gfx::BufferFormat format);
+  void Flush() override {}
 
  protected:
   ~GLImageMemory() override;
 
   gfx::BufferFormat format() const { return format_; }
   size_t stride() const { return stride_; }
 
  private:
   const gfx::Size size_;
   const unsigned internalformat_;
   const unsigned char* memory_;
   gfx::BufferFormat format_;
   size_t stride_;
 
   DISALLOW_COPY_AND_ASSIGN(GLImageMemory);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_IMAGE_MEMORY_H_