[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=
And before service worker or similar things, i don't think leave the timer working is acceptable for battery life. Even worse, here the timer is global timer.