Add trace events in NavigationControllerImpl::back/forward(...).

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 7e04526e5894a53823c197cb54cff0163ebfacc4..3e232d9c416186df7e5773ce46b8aa7a26ff21dc 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -586,11 +586,15 @@ bool NavigationControllerImpl::CanGoToOffset(int offset) const {
 }
 
 void NavigationControllerImpl::GoBack() {
+  TRACE_EVENT0("browser,navigation",
+               "NavigationControllerImpl::GoBack");
   // Call GoToIndex rather than GoToOffset to get the NOTREACHED() check.
   GoToIndex(GetIndexForOffset(-1));
 }
 
 void NavigationControllerImpl::GoForward() {
+  TRACE_EVENT0("browser,navigation",
+               "NavigationControllerImpl::GoForward");
   // Call GoToIndex rather than GoToOffset to get the NOTREACHED() check.
   GoToIndex(GetIndexForOffset(1));
 }