Add LowMemoryNotification to the API on Android platform....

Add LowMemoryNotification to the API on Android platform.

Android system provides a unique feature that it sends a notification to the
browser in low memory condition, and the browser cleans up cache and frees
resources. Forcing a GC in low memory condition can free DOM objects and also
can shrink the old spaces.

This patch addresses the last comment in 
http://codereview.chromium.org/173016/show

	
Mads Ager 2009/08/19 17:24:23 
I would prefer to not use the flags to signal that a compacting collection is
requested.

TBR = ager

Committed: http://code.google.com/p/v8/source/detail?r=2725

[Feng Qian, 2009-08-20 00:06:36]

TBR = ager

[Mads Ager (chromium), 2009-08-20 06:48:07]

LGTM