Prevent Lockscreen album art from activating FLAG_KEEP_SCREEN_ON

This is a small fix to the showWallpaper method, in which a power
consumption problem has been introduced. This showWallpaper method
toggles the window flag FLAG_SHOW_WALLPAPER, when album art is being
shown in Lockscreen. It is important to set pixel format to
PixelFormat.OPAQUE if flag FLAG_SHOW_WALLPAPER is not being set.

If not, an application that uses window flag FLAG_KEEP_SCREEN_ON
will prevent the keyguard from going to sleep and drain battery.

Change-Id: I1808be28047977ae5ac4dd1168ea25cac8a55a78

packages/Keyguard/src/com/android/keyguard/KeyguardViewManager.java

@@ -388,6 +388,7 @@ public class KeyguardViewManager {
         } else {
             mWindowLayoutParams.flags &= ~WindowManager.LayoutParams.FLAG_SHOW_WALLPAPER;
         }
+        mWindowLayoutParams.format = show ? PixelFormat.TRANSLUCENT : PixelFormat.OPAQUE;
 
         mViewManager.updateViewLayout(mKeyguardHost, mWindowLayoutParams);
     }