CrOS: Set max frames pending for UI from command line.

cc/thread_proxy.cc

Index: cc/thread_proxy.cc
diff --git a/cc/thread_proxy.cc b/cc/thread_proxy.cc
index e3c48c33159dfdd70098bd1a08d172bba1e946bf..41d6d90e8dbc3bbbac7ee03a084431df85d8912e 100644
--- a/cc/thread_proxy.cc
+++ b/cc/thread_proxy.cc
@@ -1121,7 +1121,10 @@ void ThreadProxy::InitializeRendererOnImplThread(
     scheduler_on_impl_thread_->setSwapBuffersCompleteSupported(
         capabilities->using_swap_complete_callback);
 
-    int maxFramesPending = FrameRateController::kDefaultMaxFramesPending;
+    int maxFramesPending = layer_tree_host_impl_->output_surface()->
+        capabilities().max_frames_pending;
+    if (maxFramesPending <= 0)
+      maxFramesPending = FrameRateController::kDefaultMaxFramesPending;
     if (layer_tree_host_impl_->output_surface()->capabilities().
             has_parent_compositor)
       maxFramesPending = 1;