[Aura] Reduce frequency of PinchUpdate events.

ui/events/gesture_detection/scale_gesture_detector.cc

Index: ui/events/gesture_detection/scale_gesture_detector.cc
diff --git a/ui/events/gesture_detection/scale_gesture_detector.cc b/ui/events/gesture_detection/scale_gesture_detector.cc
index f9e091bc6ce55204704cf144593c114f7050ca51..232a70e7d0cc1ac5ae48d65871bb3be197116f1d 100644
--- a/ui/events/gesture_detection/scale_gesture_detector.cc
+++ b/ui/events/gesture_detection/scale_gesture_detector.cc
@@ -33,7 +33,9 @@ const float kScaleFactor = .5f;
 ScaleGestureDetector::Config::Config()
     : min_scaling_touch_major(48),
       min_scaling_span(200),
-      quick_scale_enabled(true) {}
+      quick_scale_enabled(true),
+      min_pinch_update_span_delta(0) {
+}
 
 ScaleGestureDetector::Config::~Config() {}