GPU process clients can perform a "shallow" finish.

cc/trees/thread_proxy.cc

 // Copyright 2011 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 "cc/trees/thread_proxy.h"
 
 #include <string>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 1197 matching lines @@
           set_offscreen_context_provider(offscreen_context_provider);
     }
   } else if (offscreen_context_provider.get()) {
     offscreen_context_provider->VerifyContexts();
   }
 }
 
 void ThreadProxy::FinishGLOnImplThread(CompletionEvent* completion) {
   TRACE_EVENT0("cc", "ThreadProxy::FinishGLOnImplThread");
   DCHECK(IsImplThread());
-  if (layer_tree_host_impl_->resource_provider())
-    layer_tree_host_impl_->resource_provider()->Finish();
+  // Can this be a flush?

[piman, 2013/06/21 02:31:10]

I think this can be a shallow finish. The idea here is to ensure the
asynchronous readpixels have a chance to complete. See caveat in gl_renderer
though.

+  //if (layer_tree_host_impl_->resource_provider())
+  //  layer_tree_host_impl_->resource_provider()->Finish();
   completion->Signal();
 }
 
 void ThreadProxy::LayerTreeHostClosedOnImplThread(CompletionEvent* completion) {
   TRACE_EVENT0("cc", "ThreadProxy::LayerTreeHostClosedOnImplThread");
   DCHECK(IsImplThread());
   layer_tree_host_->DeleteContentsTexturesOnImplThread(
       layer_tree_host_impl_->resource_provider());
   layer_tree_host_impl_->SetNeedsBeginFrame(false);
   scheduler_on_impl_thread_.reset();
@@ skipping 185 matching lines @@
       !layer_tree_host_impl_->pending_tree()) {
     TRACE_EVENT_INSTANT0("cc", "ReleaseCommitbyActivation",
                          TRACE_EVENT_SCOPE_THREAD);
     DCHECK(layer_tree_host_impl_->settings().impl_side_painting);
     completion_event_for_commit_held_on_tree_activation_->Signal();
     completion_event_for_commit_held_on_tree_activation_ = NULL;
   }
 }
 
 }  // namespace cc