[Android] Remove the fork of GestureDetector.java

ui/events/gesture_detection/gesture_detector.cc

Index: ui/events/gesture_detection/gesture_detector.cc
diff --git a/ui/events/gesture_detection/gesture_detector.cc b/ui/events/gesture_detection/gesture_detector.cc
index 509e59e8f2cecba6c0a7b975b0260e02b2a83008..8cf76e62394e31838e32ae2b44b01858107d72b1 100644
--- a/ui/events/gesture_detection/gesture_detector.cc
+++ b/ui/events/gesture_detection/gesture_detector.cc
@@ -264,6 +264,7 @@ bool GestureDetector::OnTouchEvent(const MotionEvent& ev) {
         const float scroll_y = last_focus_y_ - focus_y;
         if (is_double_tapping_) {
           // Give the move events of the double-tap.
+          DCHECK(double_tap_listener_);
           handled |= double_tap_listener_->OnDoubleTapEvent(ev);
         } else if (always_in_tap_region_) {
           const int delta_x = static_cast<int>(focus_x - down_focus_x_);
@@ -293,6 +294,7 @@ bool GestureDetector::OnTouchEvent(const MotionEvent& ev) {
       {
         if (is_double_tapping_) {
           // Finally, give the up event of the double-tap.
+          DCHECK(double_tap_listener_);
           handled |= double_tap_listener_->OnDoubleTapEvent(ev);
         } else if (in_longpress_) {
           timeout_handler_->StopTimeout(TAP);