Framework/base: Added synchronization block to avoid race condition

Fix for the synchronization issue leading to access of an array
Index out of bounds. Issue occurs due to race condition between
removing the activities of a crashed process from history stack
and resuming a separate activity.

Change-Id: I14bb5834e778c15b674248e46fe93b0ce9f37967
HALO: keep apps in recents

Change-Id: I9ede8a1aba8d6721f077a39a31b6cc5cd8272dc2

Conflicts:
	services/java/com/android/server/am/ActivityRecord.java

Conflicts:

	core/java/android/app/Activity.java
	services/java/com/android/server/am/ActivityRecord.java