Use layout test support flag to turn on single thread compositor proxy scheduler

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index b0476c92140e9cef78a94e2b842f5ec1e16ea23b..6167af5f2bf733391e50164f75f14aaaf6d5202e 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -1415,8 +1415,9 @@ bool RenderThreadImpl::IsElasticOverscrollEnabled() {
 }
 
 bool RenderThreadImpl::UseSingleThreadScheduler() {
-  base::CommandLine* cmd = base::CommandLine::ForCurrentProcess();
-  return !cmd->HasSwitch(switches::kDisableSingleThreadProxyScheduler);
+  // TODO(enne): using the scheduler introduces additional composite steps
+  // that create flakiness.  This should go away eventually.
+  return !layout_test_mode_;
 }
 
 uint32 RenderThreadImpl::GetImageTextureTarget() {