NavigationTiming: set navigationStart for navigations in new tabs.

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 495f8d2a67fca4e51351e04771e2aaa72952b404..9962700bce05e7fe4695925ebe387a5c0ac65037 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -881,8 +881,8 @@ void RenderFrameImpl::OnNavigate(const FrameMsg_Navigate_Params& params) {
 
     frame->loadRequest(request);
 
-    // If this is a cross-process navigation, the browser process will send
-    // along the proper navigation start value.
+    // If this is a cross-process navigation or a navigation in a new tab, the
+    // browser process will send along the proper navigation start value.
     if (!params.browser_navigation_start.is_null() &&
         frame->provisionalDataSource()) {
       // browser_navigation_start is likely before this process existed, so we