cc: Start commit early and block on tree activation

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 73cc55787037b4b6ed0961d258f72b7864d4b1b9..6a0cf1622b19040308dc3f62f08f621997f7a36c 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -433,6 +433,13 @@ void ThreadProxy::OnHasPendingTreeStateChanged(bool has_pending_tree) {
       has_pending_tree,
       layer_tree_host_impl_->active_tree() ?
           !layer_tree_host_impl_->active_tree()->root_layer() : true);
+
+  if (!has_pending_tree && !deferred_start_commit_on_impl_thread_.is_null()) {
+    Proxy::ImplThreadTaskRunner()->PostTask(
+        FROM_HERE,
+        deferred_start_commit_on_impl_thread_);
+    deferred_start_commit_on_impl_thread_.Reset();
+  }
 }
 
 void ThreadProxy::SetNeedsCommitOnImplThread() {
@@ -880,6 +887,19 @@ void ThreadProxy::StartCommitOnImplThread(
     return;
   }
 
+  // We defer forced commits while there is a pending tree here.

[Sami, 2013/08/13 15:56:02]

Could this be done in the state machine instead? Seems like it has all the
necessary bits of information already.

[brianderson, 2013/09/07 01:18:54]

Hmm, I'll give that a try. I did it this way because I knew for sure that we
haven't affected state on the impl-thread at this point yet. Doing it in the
scheduler would allow us to defer the commit even later into the process.

+  if (layer_tree_host_impl_->pending_tree()) {
+    TRACE_EVENT0("cc", "EarlyOut_DeferringDueToPendingTree");
+    DCHECK(deferred_start_commit_on_impl_thread_.is_null());
+    deferred_start_commit_on_impl_thread_ =
+        base::Bind(&ThreadProxy::StartCommitOnImplThread,
+                   impl_thread_weak_ptr_,
+                   completion,
+                   raw_queue,
+                   offscreen_context_provider);
+    return;
+  }
+
   scoped_ptr<ResourceUpdateQueue> queue(raw_queue);
 
   if (offscreen_context_provider.get())