cc: Add some tracing for navigation events in cc.

R=ericrk@chromium.org

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I03fa2d870efcdd7f63122dd8c3d68826faeb4c0f
Reviewed-on: https://chromium-review.googlesource.com/879921Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#531770}

cc/scheduler/compositor_timing_history.cc

@@ -982,6 +982,8 @@ void CompositorTimingHistory::SetTreePriority(TreePriority priority) {
 }
 
 void CompositorTimingHistory::ClearHistoryOnNavigation() {
+  TRACE_EVENT0("cc", "CompositorTimingHistory::ClearHistoryOnNavigation");
+
   begin_main_frame_queue_duration_history_.Clear();
   begin_main_frame_queue_duration_critical_history_.Clear();
   begin_main_frame_queue_duration_not_critical_history_.Clear();

cc/trees/layer_tree_host.cc

@@ -333,6 +333,7 @@ void LayerTreeHost::FinishCommitOnImplThread(
   // the |content_source_id_| on the sync tree.
   bool did_navigate = content_source_id_ != sync_tree->content_source_id();
   if (did_navigate) {
+    TRACE_EVENT0("cc", "LayerTreeHost::DidNavigate");
     proxy_->ClearHistoryOnNavigation();
     host_impl->ClearImageCacheOnNavigation();
   }