Add to time to suspend in FlipThreadRoots to histogram

Add the time to suspend to the suspend_all_historam_ to determine if
GC pauses are caused by GC or bad mutator activity.

Also exclude ThreadFlipBegin time being counted as paused since it
happens before threads are suspended.

Test: test-art-host

Change-Id: Ia55db0ebbdc7ba6f23d7212c0e42c7806b297c2b
1 file changed