Remove DeferBackgroundExtensionCreation field trial and supporting code

Remove DeferBackgroundExtensionCreation field trial and supporting code.

This is mostly just "Revert 221621 This defers starting background
extension page RenderViews..." on trunk after resolving conflicts.

r221621 assumes a browser is always created with
StartupBrowserCreatorImpl. However, this is not true for incognito
browsers, some command line switch options, nor some launch flows via
the App Launcher. This meant that background extensions were sometimes
never created.

The field trial setup also needs to be revised, since
it went out to 50x the users that is normal for a field trial on stable
channel.

Field trial is now disabled server-side in m31-33, but there should be
enough data collected in m31 to make a call on whether to attempt this
again with fixes.

This reverts commit 736f456664be5e47df88bf8f936f40ddee299bd1.

> This defers starting background extension page RenderViews
> until after session restore has completed.
>
> This is mainly to help login/startup times so that Chrome is useful to
> the user earlier.  To make sure that this is actually helping, this CL
> includes a Finch experiment that will only enable the deferral on 50%
> of the clients.
>
> It is also expected that deferring these will help with some problems
> we've seen when extensions attempt to do GAIA authentication.
>
> BUG=279427, 259791
> TEST=Ran performance tests on ChromeOS and Linux
>
> Review URL: https://chromiumcodereview.appspot.com/23618014

Some conflicts. Most due to
c/b/e/chrome/browser/extensions/extension_process_manager.* moving to
extensions/browser/process_manager.*, and some minor ones elsewhere.

BUG=320787, 288259, 304453
R=mpcomplete@chromium.org, gspencer@chromium.org
TBR=sky@chromium.org, rlp@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=240061

[tapted, 2013-12-10 06:50:13]

Hi Matt, this is just a revert, but it's been a while. Could you take a look?

[Matt Perry, 2013-12-10 18:05:53]

gspencer: fyi

lgtm

[Greg Spencer (Chromium), 2013-12-10 18:08:50]

lgtm

[tapted, 2013-12-11 06:43:24]

TBR some owners since this is just a revert (although an old one).
 + sky for chrome/browser from the original CL
 + rlp for chrome/browser/profiles

(these parts are just deleting code)

[commit-bot: I haz the power, 2013-12-11 06:44:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tapted@chromium.org/111253003/20001

[commit-bot: I haz the power, 2013-12-11 09:13:52]

Change committed as 240061

[achuithb, 2013-12-17 19:52:05]

On 2013/12/11 09:13:52, I haz the power (commit-bot) wrote:
> Change committed as 240061

I believe this also fixes
https://code.google.com/p/chromium/issues/detail?id=304442

Great work, Trent!