Enable partial texture upload support for browser compositor with Surfaces

cc/trees/layer_tree_host_impl.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/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 272 matching lines @@
   // by the main thread, so the active tree needs to be updated as if these sent
   // values were applied and committed.
   if (CommitEarlyOutHandledCommit(reason)) {
     active_tree_->ApplySentScrollAndScaleDeltasFromAbortedCommit();
     active_tree_->ResetContentsTexturesPurged();
   }
 }
 
 void LayerTreeHostImpl::BeginCommit() {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::BeginCommit");
+  DCHECK(output_surface_);

[danakj, 2015/01/08 21:04:34]

nit: no need to dcheck, we'll crash if it's null on the next line.

why is this at begin commit instead of commitcomplete? (you want this to be
before the pending tree starts to update things right?)

+  output_surface_->ForceReclaimResources();
 
   if (UsePendingTreeForSync())
     CreatePendingTree();
 }
 
 void LayerTreeHostImpl::CommitComplete() {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::CommitComplete");
 
   if (pending_tree_)
     pending_tree_->ApplyScrollDeltasSinceBeginMainFrame();
@@ skipping 3174 matching lines @@
 }
 
 void LayerTreeHostImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   std::vector<PictureLayerImpl*>::iterator it =
       std::find(picture_layers_.begin(), picture_layers_.end(), layer);
   DCHECK(it != picture_layers_.end());
   picture_layers_.erase(it);
 }
 
 }  // namespace cc