Prevent Widgets from being retained by the MotionEventGenerator after a pause. Fixes #1728 (#1811)

Author: bluemarvin

app/src/common/shared/org/mozilla/vrbrowser/VRBrowserActivity.java

@@ -363,6 +363,7 @@ protected void onPause() {
 
     @Override
     protected void onResume() {
+        MotionEventGenerator.clearDevices();
         mWidgetContainer.getViewTreeObserver().addOnGlobalFocusChangeListener(globalFocusListener);
         if (mOffscreenDisplay != null) {
             mOffscreenDisplay.onResume();

app/src/common/shared/org/mozilla/vrbrowser/input/MotionEventGenerator.java

@@ -132,4 +132,8 @@ public static void dispatchScroll(Widget aWidget, int aDevice, float aX, float a
         device.mCoords[0].setAxisValue(MotionEvent.AXIS_VSCROLL, 0.0f);
         device.mCoords[0].setAxisValue(MotionEvent.AXIS_HSCROLL, 0.0f);
     }
+
+    public static void clearDevices() {
+        devices.clear();
+    }
 }