Set the unique_event_id when converting from TouchEvent to WebTouchEvent

ui/events/gestures/motion_event_aura_unittest.cc

Index: ui/events/gestures/motion_event_aura_unittest.cc
diff --git a/ui/events/gestures/motion_event_aura_unittest.cc b/ui/events/gestures/motion_event_aura_unittest.cc
index 8decac0bc198a35eecc5416fb5f5d6533cc24019..7b3bcdf2305722d7f753c74cb748db7a155ac4c8 100644
--- a/ui/events/gestures/motion_event_aura_unittest.cc
+++ b/ui/events/gestures/motion_event_aura_unittest.cc
@@ -490,4 +490,22 @@ TEST(MotionEventAuraTest, IgnoresStationaryMoves) {
   EXPECT_FALSE(event.OnTouch(move1));
 }
 
+// Test after converting touch events into motion events, motion events should
+// have the same unique_event_id as touch events.
+TEST(MotionEventAuraTest, UniqueEventID) {
+  MotionEventAura event;
+
+  TouchEvent press0 = TouchWithType(ET_TOUCH_PRESSED, 3);
+  EXPECT_TRUE(event.OnTouch(press0));
+  EXPECT_EQ(MotionEvent::ACTION_DOWN, event.GetAction());
+  ASSERT_EQ(1U, event.GetPointerCount());
+  EXPECT_EQ(event.GetUniqueEventId(), press0.unique_event_id());
+
+  TouchEvent press1 = TouchWithType(ET_TOUCH_PRESSED, 6);
+  EXPECT_TRUE(event.OnTouch(press1));
+  EXPECT_EQ(MotionEvent::ACTION_POINTER_DOWN, event.GetAction());
+  EXPECT_EQ(2U, event.GetPointerCount());
+  EXPECT_EQ(event.GetUniqueEventId(), press1.unique_event_id());
+}
+
 }  // namespace ui