FIX Null Pointer Exception on dialog cancel

Null Pointer Exception occurs because mWebViewCore instance
is made to null while calling destroyJava(). When
1.webview hosting activity goest to background, without calling webview onPause().
2. If app is launched again (having launchmode:singletask ) and another activity (not  webview hosting) comes on top top.
3. It destorys the previous activity holding webview which internally tries to cancel the dialog, but webviewcore instance is null.
Null pointer exception is raised.

Change-Id: Idbcd30d0b0d4a35819444bbaa5c73cced8bb35a3
Signed-off-by: Amit Kumar <amitkecian@gmail.com>
PWM: disable HW overlays for PIE

SurfaceFlinger wont wake up the GPU in SysUI's fullscreen state,
probably because it does not occupy any tangible region. That sets poor
PIE into software rendering, which has bad effects on transparency and
mdp compositioning. Disabling HW overlays as long as PIE is active seems
like a good alternative for now.

Change-Id: Ie7ed720edc5bbdd0cfb79c34a22996cf15fcd79b