cc: Setup API to release OutputSurface from LTHClient.

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 9fac98bb3490af63272a63cdcee171987260f85d..fdc19de2fe91e624e3d8abd1aab67485b9a671d0 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -217,6 +217,19 @@ void ThreadProxy::SetOutputSurface(scoped_ptr<OutputSurface> output_surface) {
                  impl_thread_weak_ptr_, base::Passed(&output_surface)));
 }
 
+scoped_ptr<OutputSurface> ThreadProxy::ReleaseOutputSurface() {

[danakj, 2015/09/17 18:43:55]

Can you DCHECK that LTH knows the OS is lost?

+  DCHECK(IsMainThread());
+  DebugScopedSetMainThreadBlocked main_thread_blocked(this);
+  CompletionEvent completion;
+  scoped_ptr<OutputSurface> output_surface;
+  Proxy::ImplThreadTaskRunner()->PostTask(
+      FROM_HERE,
+      base::Bind(&ThreadProxy::ReleaseOutputSurfaceOnImplThread,
+                 impl_thread_weak_ptr_, &completion, &output_surface));
+  completion.Wait();
+  return output_surface.Pass();

[danakj, 2015/09/17 18:43:55]

don't need Pass() on return

+}
+
 void ThreadProxy::DidInitializeOutputSurface(
     bool success,
     const RendererCapabilities& capabilities) {
@@ -1082,6 +1095,17 @@ void ThreadProxy::InitializeOutputSurfaceOnImplThread(
     impl().scheduler->DidCreateAndInitializeOutputSurface();
 }
 
+void ThreadProxy::ReleaseOutputSurfaceOnImplThread(
+    CompletionEvent* completion,
+    scoped_ptr<OutputSurface>* output_surface) {
+  TRACE_EVENT0("cc", "ThreadProxy::ReleaseOutputSurfaceOnImplThread");

[danakj, 2015/09/17 18:43:55]

we didn't trace in the STP, i think i'd rather the trace be in LTHI.

+  DCHECK(IsImplThread());
+
+  impl().scheduler->DidLoseOutputSurface();

[danakj, 2015/09/17 18:43:55]

Can you comment saying that, unlike in DidLoseOutputSurfaceOnImplThread, we
don't need to call LayerTreeHost::DidLoseOutputSurface since it already knows?

+  *output_surface = impl().layer_tree_host_impl->ReleaseOutputSurface();
+  completion->Signal();
+}
+
 void ThreadProxy::FinishGLOnImplThread(CompletionEvent* completion) {
   TRACE_EVENT0("cc", "ThreadProxy::FinishGLOnImplThread");
   DCHECK(IsImplThread());