Add support for EXT_image_flush_external extension

ui/gl/gl_image_io_surface.h

 // Copyright 2013 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_IO_SURFACE_H_
 #define UI_GL_GL_IMAGE_IO_SURFACE_H_
 
 #include <CoreVideo/CVPixelBuffer.h>
 #include <IOSurface/IOSurface.h>
 #include <stdint.h>
@@ skipping 38 matching lines @@
   void ReleaseTexImage(unsigned target) override {}
   bool CopyTexImage(unsigned target) override;
   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;
+  void Flush() override {}
   void OnMemoryDump(base::trace_event::ProcessMemoryDump* pmd,
                     uint64_t process_tracing_id,
                     const std::string& dump_name) override;
   bool EmulatingRGB() const override;
 
   gfx::GenericSharedMemoryId io_surface_id() const { return io_surface_id_; }
   base::ScopedCFTypeRef<IOSurfaceRef> io_surface();
   base::ScopedCFTypeRef<CVPixelBufferRef> cv_pixel_buffer();
 
   // Whether checking IOSurfaceIsInUse() will actually provide a meaningful
@@ skipping 26 matching lines @@
   base::ScopedCFTypeRef<CVPixelBufferRef> cv_pixel_buffer_;
   gfx::GenericSharedMemoryId io_surface_id_;
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(GLImageIOSurface);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_IMAGE_IO_SURFACE_H_