gpu: Allow fences to check whether a flush has occurred

gpu/command_buffer/service/mailbox_synchronizer.cc

 // 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.
 
 #include "gpu/command_buffer/service/mailbox_synchronizer.h"
 
 #include "base/bind.h"
 #include "gpu/command_buffer/service/mailbox_manager.h"
 #include "gpu/command_buffer/service/texture_manager.h"
 
@@ skipping 132 matching lines @@
 
     } else {
       linked_ptr<TextureGroup> group = make_linked_ptr(new TextureGroup(
           TextureDefinition(target_name.target, texture, 1, NULL)));
 
       // Unlink other textures from this mailbox in case the name is not new.
       ReassociateMailboxLocked(target_name, group.get());
       textures_.insert(std::make_pair(texture, TextureVersion(group)));
     }
   }
-  // Make sure all write fences are flushed.
-  glFlush();
 }
 
 void MailboxSynchronizer::UpdateTextureLocked(Texture* texture,
                                               TextureVersion& texture_version) {
   lock_.AssertAcquired();
   gfx::GLImage* gl_image = texture->GetLevelImage(texture->target(), 0);
   TextureGroup* group = texture_version.group.get();
   scoped_refptr<NativeImageBuffer> image_buffer = group->definition.image();
 
   // Make sure we don't clobber with an older version
@@ skipping 30 matching lines @@
           definition.IsOlderThan(it->second.version))
         continue;
       it->second.version = definition.version();
       definition.UpdateTexture(texture);
     }
   }
 }
 
 }  // namespace gles2
 }  // namespace gpu