[page_load_metrics] Get navigation_start from NavigationHandle

content/public/browser/navigation_handle.h

Index: content/public/browser/navigation_handle.h
diff --git a/content/public/browser/navigation_handle.h b/content/public/browser/navigation_handle.h
index 3b2bbadda772a2f31a97b5faff489b0b730728c9..7d022bd2fc68e26b15a3e134194e141d88068a2c 100644
--- a/content/public/browser/navigation_handle.h
+++ b/content/public/browser/navigation_handle.h
@@ -39,6 +39,10 @@ class CONTENT_EXPORT NavigationHandle {
   // The WebContents the navigation is taking place in.
   WebContents* GetWebContents();
 
+  // The time the navigation started, recorded either in the renderer or browser

[clamy, 2015/11/09 13:09:53]

nit: in the browser process...

[Charlie Harrison, 2015/11/09 18:45:10]

Can you clarify this comment?

[kinuko, 2015/11/12 20:35:11]

"... in the renderer or in the browser process" I guess.

+  // process. Corresponds to Navigation Timing API Standard.

[clamy, 2015/11/09 13:09:53]

nit: the Navigation Timing API Standard?

[Charlie Harrison, 2015/11/09 18:45:10]

Done.

+  virtual const base::TimeTicks& GetNavigationStart() = 0;
+
   // Parameters available at network request start time ------------------------
   //
   // The following parameters are only available when the network request is