[Aura] Reduce frequency of PinchUpdate events.

ui/events/gesture_detection/gesture_provider.cc

Index: ui/events/gesture_detection/gesture_provider.cc
diff --git a/ui/events/gesture_detection/gesture_provider.cc b/ui/events/gesture_detection/gesture_provider.cc
index 7607f08d8765a7fbc02a96f7eb471af5f813efcb..1f57adf2f96de7841ea038c3bff999e933fd9c10 100644
--- a/ui/events/gesture_detection/gesture_provider.cc
+++ b/ui/events/gesture_detection/gesture_provider.cc
@@ -130,7 +130,9 @@ class GestureProvider::ScaleGestureListenerImpl
       : scale_gesture_detector_(config, this),
         provider_(provider),
         ignore_multitouch_events_(false),
-        pinch_event_sent_(false) {}
+        pinch_event_sent_(false),
+        min_pinch_update_span_delta_(config.min_pinch_update_span_delta),
+        prev_span_(0) {}
 
   bool OnTouchEvent(const MotionEvent& event) {
     // TODO: Need to deal with multi-touch transition.
@@ -171,6 +173,16 @@ class GestureProvider::ScaleGestureListenerImpl
                        const MotionEvent& e) OVERRIDE {
     if (ignore_multitouch_events_ && !detector.InDoubleTapMode())
       return false;
+
+    float span = detector.GetCurrentSpan();
+    bool pinch_occured =

[jdduke (slow), 2014/05/22 17:37:24]

Hmm, why are you doing this before the if (!pinch_event_sent_) check? I thought
that's the whole reason we moved this logic here, so that we could get the
PINCH_BEGIN without the PINCH_UPDATE?

I would move this down, before the scale check. Then, just return false if it
fails the threshold test, and use the |GetPreviousSpan()| value from the
ScaleGestureDetector.

[tdresser, 2014/05/22 17:57:22]

Done.

+        std::abs(span - prev_span_) >= min_pinch_update_span_delta_;
+
+    if (!pinch_occured)
+      return true;
+
+    prev_span_ = span;
+
     if (!pinch_event_sent_) {
       pinch_event_sent_ = true;
       provider_->Send(CreateGesture(ET_GESTURE_PINCH_BEGIN,
@@ -247,6 +259,12 @@ class GestureProvider::ScaleGestureListenerImpl
   // Whether any pinch zoom event has been sent to native.
   bool pinch_event_sent_;
 
+  // The minimum change in span required before this is considered a pinch. See
+  // crbug.com/373318.
+  float min_pinch_update_span_delta_;
+
+  float prev_span_;

[jdduke (slow), 2014/05/22 17:37:24]

See comment above, we shouldn't need to cache the prev_span_.

[tdresser, 2014/05/22 17:57:22]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(ScaleGestureListenerImpl);
 };