Add support for KeyboardEvent.location attribute

Add support for KeyboardEvent.location attribute as per the latest specification:
http://dev.w3.org/2006/webapi/DOM-Level-3-Events/html/DOM3-Events.html#events-KeyboardEvent

IE10 and Firefox 22 both support KeyboardEvent.location already.

KeyboardEvent.keyLocation is now marked as deprecated so as to not break backward
compatibility and so that we can track its usage.

The V8 bindings generator was extended to better support [ImplementedAs] and
[DeprecateAs] extended attribute for attributes that have
[InitializedByEventConstructor] extended attribute.

Note that several other attributes of KeyboardEvent still don't match the
specification.

BUG=263308
R=arv@chromium.org, darin@chromium.org, garykac@chromium.org, haraken@chromium.org, ojan@chromium.org, pfeldman@chromium.org

Review URL: https://codereview.chromium.org/20034002

git-svn-id: svn://svn.chromium.org/blink/trunk@155170 bbb929c8-8fbe-4397-9dbb-9b2b20218538