Only allow touch events from one device at a time.

Reject movements from other devices when one device is already down.
This fixes jittery behavior when the user moves the mouse and touches
the screen at the same time.

Change-Id: I99151c8f2596a3139720f776bcbc559d4b314878
diff --git a/services/input/InputDispatcher.h b/services/input/InputDispatcher.h
index 7305601..c8beab2 100644
--- a/services/input/InputDispatcher.h
+++ b/services/input/InputDispatcher.h
@@ -957,6 +957,7 @@
     struct TouchState {
         bool down;
         bool split;
+        int32_t deviceId; // id of the device that is currently down, others are rejected
         Vector<TouchedWindow> windows;
 
         TouchState();