Fix blank page activity selection bug

 Bug: 5191031
 Sets an app id on the tab so that if the intent comes back to us,
 it is opened in the current tab.
 Close empty tabs correctly if the intent goes elsewhere
 Fix Tab.syncCurrentState to deal with WebView.getUrl() == null correctly

Change-Id: I31e1e1f6688fb5c5c31ba07dde4e6b3bad34fb13
3 files changed