Bug 1024463 - Define an out of line destructor for TextTrackCue so that we can forward delcare HTMLTrackElement in TextTrackCue.h; r=bzbarsky

This is required because the destructor for the nsRefPtr<HTMLTrackElement>
member requires the full definition of the type.
Bug 1024465 - Define an out of line destructor for DataStore so that we can forward delcare DataStoreImpl in DataStore.h; r=bzbarsky

This is required because the destructor for the nsRefPtr<DataStoreImpl>
member requires the full definition of the type.