Cherry pick Refactor ActivityManagerService and make WebViewFactory more pedantic. DO NOT MERGE

This CL adds more robustness to the logic in WebViewFactory, checking
whether the isolated process did start at all and catching exceptions
in its java side.
Also, this addresses the refactor comments received in CL 509840.

Original BUG:16403706
Original Change-Id: Iaaea6d36142ece6d974c2438259edf421fce9f2e

Bug: 16723226
Change-Id: Id308f2ffde9b67a3eb4719c7b81b4f46421f0c2e