Invalid press events don't create multiple pointers with the same id.

Previously if we got an invalid event stream such as

Press id 0
Press id 0

MotionEventAura would happily add the second pointer. Now we replace
the first pointer with the second pointer.

This work around is required due to crbug.com/373125.

BUG=450880

Review URL: https://codereview.chromium.org/873283003

Cr-Commit-Position: refs/heads/master@{#313116}
(cherry picked from commit b88d572)

Review URL: https://codereview.chromium.org/867823005

Cr-Commit-Position: refs/branch-heads/2272@{#185}
Cr-Branched-From: 827a380-refs/heads/master@{#310958}

ui/aura/gestures/gesture_recognizer_unittest.cc

@@ -2554,7 +2554,7 @@ TEST_F(GestureRecognizerTest, PressDoesNotCrash) {
   // there is at least one case where we need to allow a touch press
   // from a currently used touch id. See crbug.com/373125 for details.
   EXPECT_TRUE(delegate->begin());
-  EXPECT_FALSE(delegate->tap_down());
+  EXPECT_TRUE(delegate->tap_down());
   EXPECT_TRUE(delegate->tap_cancel());
   EXPECT_FALSE(delegate->scroll_begin());
 }

ui/events/gestures/motion_event_aura.cc

@@ -74,12 +74,17 @@ bool MotionEventAura::OnTouch(const TouchEvent& touch) {
   bool pointer_id_is_active = index != -1;
 
   if (touch.type() == ET_TOUCH_PRESSED && pointer_id_is_active) {
-    // Ignore touch press events if we already believe the pointer is down.
-
-    // TODO(tdresser): this should return false (or NOTREACHED());
-    // however, there is at least one case where we need to allow a
-    // touch press from a currently used touch id. See
+    // TODO(tdresser): This should return false (or NOTREACHED()), and
+    // ignore the touch; however, there is at least one case where we
+    // need to allow a touch press from a currently used touch id. See
     // crbug.com/446852 for details.
+
+    // Cancel the existing touch, before handling the touch press.
+    TouchEvent cancel(ET_TOUCH_CANCELLED, touch.location(), touch.touch_id(),
+                      touch.time_stamp());
+    OnTouch(cancel);
+    CleanupRemovedTouchPoints(cancel);
+    DCHECK_EQ(-1, FindPointerIndexOfId(touch.touch_id()));
   } else if (touch.type() != ET_TOUCH_PRESSED && !pointer_id_is_active) {
     // We could have an active touch stream transfered to us, resulting in touch
     // move or touch up events without associated touch down events. Ignore

ui/events/gestures/motion_event_aura_unittest.cc

@@ -426,10 +426,20 @@ TEST(MotionEventAuraTest, Flags) {
 
 // Once crbug.com/446852 is fixed, we should ignore redundant presses.
 TEST(MotionEventAuraTest, DoesntIgnoreRedundantPresses) {
-  int id = 7;
+  const int id = 7;
+  const int position_1 = 10;
+  const int position_2 = 23;
+
   MotionEventAura event;
-  EXPECT_TRUE(event.OnTouch(TouchWithType(ET_TOUCH_PRESSED, id)));
-  EXPECT_TRUE(event.OnTouch(TouchWithType(ET_TOUCH_PRESSED, id)));
+  TouchEvent press1 = TouchWithPosition(ET_TOUCH_PRESSED, id, position_1,
+                                        position_1, position_1, position_1);
+  EXPECT_TRUE(event.OnTouch(press1));
+  TouchEvent press2 = TouchWithPosition(ET_TOUCH_PRESSED, id, position_2,
+                                        position_2, position_2, position_2);
+  EXPECT_TRUE(event.OnTouch(press2));
+
+  EXPECT_EQ(1U, event.GetPointerCount());
+  EXPECT_FLOAT_EQ(position_2, event.GetX(0));
 }
 
 TEST(MotionEventAuraTest, IgnoresEventsWithoutPress) {