Add support for EXT_image_flush_external extension

gpu/command_buffer/service/texture_manager_unittest.cc

 // Copyright (c) 2012 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.
 
 #include "gpu/command_buffer/service/texture_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
@@ skipping 149 matching lines @@
                        const gfx::Rect& rect) override {
     return false;
   }
   bool ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
                             int z_order,
                             gfx::OverlayTransform transform,
                             const gfx::Rect& bounds_rect,
                             const gfx::RectF& crop_rect) override {
     return false;
   }
+  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 { return false; }
   void GetTextureMatrix(float matrix[16]) override {}
 
  protected:
   ~GLStreamTextureImageStub() override {}
 };
 
@@ skipping 2565 matching lines @@
   ExpectValid(
       true, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8, GL_DEPTH24_STENCIL8);
   ExpectValid(true, GL_DEPTH_STENCIL, GL_FLOAT_32_UNSIGNED_INT_24_8_REV,
               GL_DEPTH32F_STENCIL8);
 
   ExpectInvalid(true, GL_RGB_INTEGER, GL_INT, GL_RGBA8);
 }
 
 }  // namespace gles2
 }  // namespace gpu