Bug 975346 - Part 1: General functions for Effects. r=dglastonbury

1. Support GenEffectChain() for LayerComposite.
   Each layer can use this API to gen the
   EffectChain (only primary effect now)
2. Support GenEffect() for CompositableHost.
3. Move AutoLock to compositeHost.
Bug 975346 - Part 2: Support LayerScope for HwcComposer2D. r=dglastonbury

1. Retrieve buffer from GPU.
2. Refactor - use SenderHelper class to manage the Sender
   static function structure.
Bug 1018933 - Part 1: HTMLTrackElement should not create another TextTrack if one already exists. r=rillian
Bug 1018933 - Part 2: Add regression test. r=rillian