Prewarm WebView renderer when in multiprocess mode.

Prewarm WebView renderer when in multiprocess mode.

When we're in multiprocess mode, prewarm the renderer process early in
browser startup in the same way Chrome does. This reduces the startup
time penalty of multiprocess WebView by almost half in simple local
tests on a Nexus 6P.

BUG=653560
Committed: https://crrev.com/53cb8b57b2ba954bbce9fbe0503d127c565b1670
Cr-Commit-Position: refs/heads/master@{#423569}

[Torne, 2016-10-06 15:24:04]

torne@chromium.org changed reviewers:
+ tobiasjs@chromium.org

[Torne, 2016-10-06 15:24:05]

On my N6P with stock Android 7.0 running the trivial startup test in the system
webview shell, the regression from multiprocess without my change is about 60ms,
but with this change it's about 30ms.

[Robert Sesek, 2016-10-06 16:21:51]

rsesek@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2016-10-06 16:21:52]

lgtm

[Tobias Sargeant, 2016-10-06 16:55:20]

lgtm

[Torne, 2016-10-06 16:58:10]

The CQ bit was checked by torne@chromium.org

[commit-bot: I haz the power, 2016-10-06 16:58:41]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-06 17:22:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-06 17:24:35]

Description was changed from

==========
Prewarm WebView renderer when in multiprocess mode.

When we're in multiprocess mode, prewarm the renderer process early in
browser startup in the same way Chrome does. This reduces the startup
time penalty of multiprocess WebView by almost half in simple local
tests on a Nexus 6P.

BUG=653560
==========

to

==========
Prewarm WebView renderer when in multiprocess mode.

When we're in multiprocess mode, prewarm the renderer process early in
browser startup in the same way Chrome does. This reduces the startup
time penalty of multiprocess WebView by almost half in simple local
tests on a Nexus 6P.

BUG=653560

Committed: https://crrev.com/53cb8b57b2ba954bbce9fbe0503d127c565b1670
Cr-Commit-Position: refs/heads/master@{#423569}
==========

[commit-bot: I haz the power, 2016-10-06 17:24:36]

Patchset 1 (id:??) landed as
https://crrev.com/53cb8b57b2ba954bbce9fbe0503d127c565b1670
Cr-Commit-Position: refs/heads/master@{#423569}