[webkit] Runtime enablement of WebGL

Hook up debug setting to enable/disable WebGL.

Change-Id: I46790e61471a76eb5a8d8ff552022e12c3782204
webkit: Multimedia feature port from ICS

- Multi-context HTML5 video support
- Smooth inline to fullscreen video transition
- Support for autoplay, muted, loop, preload attributes
- Support for web pages with more than one audio element
- Support for HTTP live streaming

Change-Id: I82b01295da4663437d5c35eb45d145b243ecc9f1

webkit: HTML5 video user experience and stability fixes

- Fix HTML5 video unable to resume from navigation history
- Fix occasional crash when reloading page from history
- Show last decoded frame of streaming video when buffering
- Fix incorrect fullscreen video position during orientation change
- Replace HTML5VideoView resetted state with released state
- Remove unneeded videoLayerId in HTML5VideoView
- Resume from last played position after video suspend
- Call MediaController::show() during HTML5VideoView play and pause
  to update fullscreen MediaController state

Change-Id: I82f1255225b2ee6cc95f70e40017d562e5e635c6

webkit: Fix black screen shown during webkit exitFullscreen

Notify WebChromeClient to hide custom view during exit fullscreen.

CRs-fixed: 387484

Change-Id: If67cc000991d9fa0696692ce3982e0a04499e343