A different approach to fixing FirstWebContentsProfiler with PlzNavigate.

A different approach to fixing FirstWebContentsProfiler with PlzNavigate.

The previous fix depended on ensuring we add hooks to all the code paths that cause the first active WebContents to get added to the tab strip. We're still missing some code paths. So instead restore the old behavior. Even though it did miss navigation starts, fix that by using the time from NavigationHandle for PlzNavigate.

This should restore the metrics for non-PlzNavigate case.
For PlzNavigate, the start timings were already different regardless from non-PlzNavigate because of how navigations are structured very differently. This change shouldn't affects things too much for PlzNavigate though, because the only difference should be the IPC time from the renderer to the browser thread.

BUG=650349
Review-Url: https://codereview.chromium.org/2448553002
Cr-Commit-Position: refs/heads/master@{#427144}
(cherry picked from commit f4ba53f555685c67fc3fb4ffdb18c4ff7baea19c)

[jam, 2016-10-26 23:13:14]

Committed patchset #1 (id:1) to pending queue manually as
9b8c9827bad151ac34cbb5900a554d96186e334b.