DO NOT MERGE: Adding freeMemoryForTests static method to WebView.

This is going to be used by pagecycler tests.
See: b/10629847

Change-Id: Ie3fda214e7808429d7ed63734ab301525f58513f
(cherry pick of 24426750)

Cherry pick to klp-dev as part of Bug: 13246014

Conflicts:
	core/java/android/webkit/WebViewClassic.java
	core/java/android/webkit/WebViewFactoryProvider.java
(cherry picked from commit 54daaf1cffddad6366fac2ccfceb1e042dd8e90e)

Change-Id: I8471ee5cfaac2ff72704c2391a1961f441aaa1e6