Fix issue #3387676 com.android.browser: java.lang.NullPointerException...

Unable to destroy activity {com.android.browser/com.android.browser.BrowserActivity}:
java.lang.NullPointerException at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:2809)

Add a bunch of guards to not call on to the window callback after the
window is destroyed.

Change-Id: I66ca0705f421bafdfe953d03654c8f78d9e68249
1 file changed