EQT: Record the max queueing time from navigation start to navigation away

third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h

Index: third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h
diff --git a/third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h b/third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h
index 65b3f5ab4feb83e9a70f03f7ee2d9cf37c19e429..56a4b03431194d7be67cc7cddcf2ee4751fe8267 100644
--- a/third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h
+++ b/third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h
@@ -153,6 +153,8 @@ class BLINK_PLATFORM_EXPORT RendererScheduler : public ChildScheduler {
   // Must be called from the main thread.
   virtual void OnNavigationStarted() = 0;
 
+  virtual void OnCommitProvisionalLoad() = 0;

[Charlie Reis, 2017/06/02 22:38:37]

This needs a comment, especially for how it differs from OnNavigationStarted. 
(I'm not clear why we need both, if they're called back-to-back.)

[Liquan (Max) Gu, 2017/06/02 23:32:06]

I am not sure about what "Commit Provisional Load" serve as a general purpose
and what it indicates, so I will call this function
OnCommitProvisionalLoadAndNavigationStarted() to be more precise, to indicate
this is signaling provisional load has been committed and navigation has
started. Is it OK?

[Charlie Reis, 2017/06/05 05:02:34]

No, sorry, I think that's more confusing.

I think we're just meaning different things when saying "navigation started." 
In the navigation logic, we refer to "start" as the time when the navigation's
network request is being made, which often unknown to the renderer process (even
more so with PlzNavigate).  "Commit" is the point at which the renderer process
starts parsing and rendering the new page, and it seems to me that's the point
in time that any renderer-side metrics should be interested in-- it's the point
that activity stops happening in the old page and starts happening in the new
page.

In that sense, I would expect us to remove OnNavigationStarted and only have
OnCommitProvisionalLoad.  If I'm following things correctly, that's the plan in
https://crbug.com/726341, and we can have comments and TODOs in this file to
that effect.

[Liquan (Max) Gu, 2017/06/05 16:15:56]

Thanks! 

+
   // Returns true if the scheduler has reason to believe that high priority work
   // may soon arrive on the main thread, e.g., if gesture events were observed
   // recently.