Reland of Call EnsureWebKitInitialized() before registering extensions

Reland of Call EnsureWebKitInitialized() before registering extensions (patchset #1 id:1 of https://codereview.chromium.org/1244243003/)

Reason for revert:
It turns out this CL isn't the culprit of crashes. Let's reland.

Original issue's description:
> Revert of Call EnsureWebKitInitialized() before registering extensions (patchset #3 id:40001 of https://codereview.chromium.org/1182083006/)
>
> Reason for revert:
> This seems the cause of many crashes
>
> Original issue's description:
> > Call EnsureWebKitInitialized() before registering extensions
> >
> > Blink needs to be initialized before registering an extension because:
> > - WebScriptController::registerExtension() allocates an WTF::Vector on the first
> >   call.
> > - WTF::Vector uses PartitionAlloc.
> > - PartitionAlloc's partitions needs to be initialized before allocating memory.
> >   Blink initialization does the job.
> >
> > Before this CL, partitions are initialized lazily but lazy initialization
> > doesn't provide proper histogram function, which might be the cause of missing
> > report for PartitionAlloc.CommittedSize UMA.
> >
> > BUG=501171
> >
> > Committed: https://crrev.com/0d244fa5e106b3d146655a2c623539a3e1900831
> > Cr-Commit-Position: refs/heads/master@{#339200}
>
> TBR=jochen@chromium.org,haraken@chromium.org,kalman@chromium.org,kinuko@chromium.org,paulmeyer@chromium.org,sievers@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=501171
>
> Committed: https://crrev.com/2b94b05fc252c9a006ae924d0fe75ed3abecbeb2
> Cr-Commit-Position: refs/heads/master@{#339777}

TBR=jochen@chromium.org,haraken@chromium.org,kalman@chromium.org,kinuko@chromium.org,paulmeyer@chromium.org,sievers@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=501171
Committed: https://crrev.com/0444616094fcba557a06eb292ebd568281f82c84
Cr-Commit-Position: refs/heads/master@{#340793}

[bashi, 2015-07-28 00:42:06]

Created Reland of Call EnsureWebKitInitialized() before registering extensions

[bashi, 2015-07-28 00:43:00]

The CQ bit was checked by bashi@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-07-28 00:43:06]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1258103005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1258103005/1

[commit-bot: I haz the power, 2015-07-28 00:43:39]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-07-28 00:43:40]

Dry run: This issue passed the CQ dry run.

[bashi, 2015-07-28 00:45:40]

jochen@, kalman@ Could you review this again? No change made.

[haraken, 2015-07-28 05:05:32]

LGTM

[jochen (gone - plz use gerrit), 2015-07-28 10:55:49]

lgtm

[not at google - send to devlin, 2015-07-28 16:47:32]

lgtm

[bashi, 2015-07-28 22:55:35]

The CQ bit was checked by bashi@chromium.org

[commit-bot: I haz the power, 2015-07-28 22:56:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1258103005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1258103005/1

[commit-bot: I haz the power, 2015-07-28 22:58:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-28 22:58:50]

Patchset 1 (id:??) landed as
https://crrev.com/0444616094fcba557a06eb292ebd568281f82c84
Cr-Commit-Position: refs/heads/master@{#340793}