[Android] React to activity state change within XWalkView

Previously, XWalkView relies on embedders to manage the
resource of XWalkView based on Activity lifecycle.

In this commit, implement XWalkView as ActivityStatusListener
and handle the lifecycle state change by itself.

BUG=
@wang16, it is no problem that `onHide` and `onShow` is called when the container activity is paused or resumed, however, for `pauseTimers` and `resumeTimers`, it would be the responsibility of the embedder, right? for example, the embedder may not want to pause timer when paused.