Bug 973345 - Include gradient values in the return value of getCSSValuesForProperty() for properties that can have an <image> value specified. r=bz
Bug 987076 - Construct HTMLMediaElement::mTextTrackManager lazily. r=roc

* Remove the TextTrackManager's initialization from the MediaElement's
ctor and add a getter that creates it if we don't have it yet. The public
functions exposed on the MediaElement's IDL now call this getter.
* Also remove the const qualifier from HTMLMediaElement::TextTracks()
as we don't really need it and this function now needs to call
GetOrCreateTextTrackManager() which is non-const.
Bug 987320 - Remove unnecessary null checks for do_QueryFrame arguments. r=bz