Re-land: cc: Implement shared worker contexts.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 48604f7e9760172cf3d48f6f48ed22696201e318..3134b3addfa73eba7ef7047773b52082edabef6d 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -388,7 +388,9 @@ void LayerTreeHost::SetOutputSurface(scoped_ptr<OutputSurface> surface) {
   DCHECK(output_surface_lost_);
   DCHECK(surface);
 
-  proxy_->SetOutputSurface(surface.Pass());
+  DCHECK(!new_output_surface_);
+  new_output_surface_ = surface.Pass();
+  proxy_->SetOutputSurface(new_output_surface_.get());

[piman, 2015/09/14 21:54:38]

Would it be possible to add a test that verifies that it's possible to destroy
the LTH after SetOutputSurface was called but before we got a
DidInitializeOutputSurface/DidFailToInitializeOutputSurface?

[reveman, 2015/09/15 20:38:35]

Done. LayerTreeHostTestDestroyWhileInitializingOutputSurface.

 }
 
 void LayerTreeHost::RequestNewOutputSurface() {
@@ -396,12 +398,20 @@ void LayerTreeHost::RequestNewOutputSurface() {
 }
 
 void LayerTreeHost::DidInitializeOutputSurface() {
+  DCHECK(new_output_surface_);
   output_surface_lost_ = false;
+  current_output_surface_ = new_output_surface_.Pass();
   client_->DidInitializeOutputSurface();
 }
 
 void LayerTreeHost::DidFailToInitializeOutputSurface() {
   DCHECK(output_surface_lost_);
+  DCHECK(new_output_surface_);
+  // Note: It is safe to drop all output surface references here as
+  // LayerTreeHostImpl will not keep a pointer to either the old or
+  // new output surface after failing to initialize the new one.
+  current_output_surface_ = nullptr;
+  new_output_surface_ = nullptr;
   client_->DidFailToInitializeOutputSurface();
 }