Make SingleThreadProxy a SchedulerClient

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 694fedbcd0909399627d73503f5d2f80ee47db33..f63daa72444d039d4a80d467415919388a865600 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -1501,6 +1501,11 @@ gfx::SizeF LayerTreeHostImpl::UnscaledScrollableViewportSize() const {
 }
 
 void LayerTreeHostImpl::DidLoseOutputSurface() {
+#ifndef NDEBUG
+  // This must be set before calling the below functions as they may
+  // synchronously try to recreate the output surface.
+  did_lose_called_ = true;
+#endif
   if (resource_provider_)
     resource_provider_->DidLoseOutputSurface();
   // TODO(jamesr): The renderer_ check is needed to make some of the
@@ -1508,9 +1513,6 @@ void LayerTreeHostImpl::DidLoseOutputSurface() {
   // important) in production. We should adjust the test to not need this.
   if (renderer_)
     client_->DidLoseOutputSurfaceOnImplThread();
-#ifndef NDEBUG
-  did_lose_called_ = true;
-#endif
 }
 
 void LayerTreeHostImpl::Readback(void* pixels,
@@ -1819,9 +1821,13 @@ bool LayerTreeHostImpl::InitializeRenderer(
       base::TimeDelta::FromMicroseconds(
           base::Time::kMicrosecondsPerSecond /
           settings_.refresh_rate);
-
+    // If no compositor thread, then begin impl frame messages should just
+    // go back to the main thread.
+    base::SingleThreadTaskRunner* task_runner =
+        proxy_->ImplThreadTaskRunner() ? proxy_->ImplThreadTaskRunner()
+                                       : proxy_->MainThreadTaskRunner();
     output_surface->InitializeBeginImplFrameEmulation(
-        proxy_->ImplThreadTaskRunner(),
+        task_runner,
         settings_.throttle_frame_production,
         display_refresh_interval);
   }