Enable touch splitting for all windows by default.

New default only applies to applications with targetSdkVersion >=
HONEYCOMB.  Old applications default to no touch splitting for
their windows.

In addition, enabled split touch for various system windows.

Bug: 3049580
Change-Id: Idc8da9baa2cd8e1e4e76af8967d7b6a5ccb94427
diff --git a/include/ui/InputDispatcher.h b/include/ui/InputDispatcher.h
index d09ff41..15a3925 100644
--- a/include/ui/InputDispatcher.h
+++ b/include/ui/InputDispatcher.h
@@ -219,6 +219,8 @@
      * motion events to be delivered to them with AMOTION_EVENT_FLAG_WINDOW_IS_OBSCURED.
      */
     bool isTrustedOverlay() const;
+
+    bool supportsSplitTouch() const;
 };
 
 
@@ -946,7 +948,7 @@
     struct TouchedWindow {
         const InputWindow* window;
         int32_t targetFlags;
-        BitSet32 pointerIds;
+        BitSet32 pointerIds;        // zero unless target flag FLAG_SPLIT is set
         sp<InputChannel> channel;
     };
     struct TouchState {