cc: Send all begin frames using a PostTask.

cc/trees/proxy_impl.cc

Index: cc/trees/proxy_impl.cc
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index f69296deb1bb8fdc9540b48093639cc3ccc68720..f4b587bf44cc6d4548483f0925d415504f61b620 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -86,15 +86,13 @@ ProxyImpl::ProxyImpl(
   BeginFrameSource* frame_source = external_begin_frame_source_.get();
   if (!scheduler_settings.throttle_frame_production) {
     // Unthrottled source takes precedence over external sources.
-    unthrottled_begin_frame_source_.reset(
-        new BackToBackBeginFrameSource(base::MakeUnique<DelayBasedTimeSource>(
-            task_runner_provider_->ImplThreadTaskRunner())));
+    unthrottled_begin_frame_source_.reset(new BackToBackBeginFrameSource(
+        task_runner_provider_->ImplThreadTaskRunner()));
     frame_source = unthrottled_begin_frame_source_.get();
   }
   if (!frame_source) {
-    synthetic_begin_frame_source_.reset(
-        new DelayBasedBeginFrameSource(base::MakeUnique<DelayBasedTimeSource>(
-            task_runner_provider_->ImplThreadTaskRunner())));
+    synthetic_begin_frame_source_.reset(new DelayBasedBeginFrameSource(
+        task_runner_provider_->ImplThreadTaskRunner()));
     frame_source = synthetic_begin_frame_source_.get();
   }
   scheduler_ =