Revert of Remove prefixed Pointer Lock API.

Revert of Remove prefixed Pointer Lock API. (https://codereview.chromium.org/424093006/)

Reason for revert:
The change broke several Chromium OS interactive_ui_tests:

ExtensionPointerLockAccessFail
ExtensionPointerLockAccessPass
EscapingMouseLock
MouseLockSilentAfterTargetUnlock
TestTabDoesntExitMouseLockOnSubFrameNavigation
TestTabExitsMouseLockOnGoBack
TestTabExitsMouseLockOnNavigation
PointerLock_PointerLockLostWithFocus

that were using the prefixed API (""Uncaught TypeError: undefined is not a function").

See
http://build.chromium.org/p/chromium.webkit/builders/Linux%20ChromiumOS%20Tests%20%282%29/builds/735/steps/interactive_ui_tests/logs/stdio

Original issue's description:
> Remove prefixed Pointer Lock API.
> 
> The Pointer Lock API http://www.w3.org/TR/pointerlock has already been
> implemented without prefix, this change removes the 'webkit' prefixed
> API endpoints.
> 
> Intent to Deprecate and Remove:
> https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/tN8fWRtG0MI
> 
> BUG=398457
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179172

TBR=abarth@chromium.org,scheib@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398457
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179186

[Julien - ping for review, 2014-07-30 00:47:59]

Created Revert of Remove prefixed Pointer Lock API.

[commit-bot: I haz the power, 2014-07-30 00:49:02]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/424213007/1

[commit-bot: I haz the power, 2014-07-30 00:50:39]

Change committed as 179186

[scheib, 2014-08-01 20:23:19]

A revert of this CL has been created in
https://codereview.chromium.org/437443005/ by scheib@chromium.org.

The reason for reverting is: Downstream tests have been updated to use
unprefixed pointer lock..