Fix Performance::now() for browser navigations.

Fix Performance::now() for browser navigations.

Performance::now() is defined[1] as number of milliseconds since
navigationStart. It works correctly for renderer-initiated navigations,
but for browser-initiated ones we override the navigationStart with the
recording taken on the browser side and this is not represented in
Performace::now().

Among other reasons to be sad about this, this bug makes Chromium's
pagecyclers not represent the renderer initialization times in their
plt measurements.

This patch fixes this by adjusting the fields that are supposed to
correspond to navigationStart when we change navigationStart from the
embedder.

[1] http://www.w3.org/TR/hr-time/#dom-performance-now

BUG=376004
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178558

[ppi, 2014-07-09 14:58:14]

Camille, Nate - ptal.

Tony - fyi.

[clamy, 2014-07-09 15:05:19]

Lgtm, thanks!

[tonyg, 2014-07-09 15:08:02]

lgtm

You might want to put a note to the perf sheriffs in the CL description that
this is expected to change the page cyclers. Might also consider a heads up to
some of the search folks as they track these things pretty closely and will want
to know the chrome version to watch for this change.

[ppi, 2014-07-21 12:06:44]

Yup, sent a heads-up. I think we would send another with broader scope if the
change sticks. See also http://crbug.com/394757 .

Thanks for the review!

[ppi, 2014-07-21 12:06:49]

The CQ bit was checked by ppi@chromium.org

[commit-bot: I haz the power, 2014-07-21 12:07:45]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ppi@chromium.org/379873002/20001

[commit-bot: I haz the power, 2014-07-21 13:16:44]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_compile_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_compile_dbg/bu...)

[commit-bot: I haz the power, 2014-07-21 13:29:16]

Change committed as 178558

[Peter Kasting, 2014-07-21 23:22:47]

A revert of this CL has been created in
https://codereview.chromium.org/409723002/ by pkasting@chromium.org.

The reason for reverting is: Broke
org.chromium.android_webview.test.AwContentsClientShouldOverrideUrlLoadingTest#testDoubleNavigateDoesNotSuppressInitialNavigate
on the Android test bots.  See http://crbug.com/395817 ..