Multimedia feature port from ICS

Support for runtime media preload configuration with 3 options:
    - Never
    - Only on WiFi (default)
    - Always

Support video transition animation

Change-Id: Idd03f5bb57d6f78ec8b8e407eba01904f392f554
Runtime enablement of WebGL

Add Labs setting for enabling and disabling WebGL. Need to make sure
WebGL has been compiled in before showing runtime enablement settings in
Labs menu. Requesting information from the native side through JNI.

Change-Id: I50e9321babaaf039e25e30f7ead6527169d32e1b