Adopt "QuickScale" double-tap drag zoom code in the GestureProvider

content/common/input/web_input_event_traits.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/input/web_input_event_traits.h"
 
 #include <bitset>
 
 #include "base/logging.h"
 
@@ skipping 127 matching lines @@
   *event = event_to_coalesce;
   for (unsigned i = 0; i < event->touchesLength; ++i) {
     int i_old = GetIndexOfTouchID(old_event, event->touches[i].id);
     if (old_event.touches[i_old].state == blink::WebTouchPoint::StateMoved)
       event->touches[i].state = blink::WebTouchPoint::StateMoved;
   }
 }
 
 bool CanCoalesce(const WebGestureEvent& event_to_coalesce,
                  const WebGestureEvent& event) {
-  return event.type == event_to_coalesce.type &&
-         event.type == WebInputEvent::GestureScrollUpdate &&
-         event.sourceDevice == event_to_coalesce.sourceDevice &&
-         event.modifiers == event_to_coalesce.modifiers;
+  if (event.type != event_to_coalesce.type ||
+      event.sourceDevice != event_to_coalesce.sourceDevice ||
+      event.modifiers != event_to_coalesce.modifiers)
+    return false;
+
+  if (event.type == WebInputEvent::GestureScrollUpdate)
+    return true;
+
+  // GesturePinchUpdate scales can be combined only if they share a focal point,
+  // e.g., with double-tap drag zoom.
+  if (event.type == WebInputEvent::GesturePinchUpdate &&
+      event.x == event_to_coalesce.x &&
+      event.y == event_to_coalesce.y)
+    return true;
+
+  return false;
 }
 
 void Coalesce(const WebGestureEvent& event_to_coalesce,
               WebGestureEvent* event) {
   DCHECK(CanCoalesce(event_to_coalesce, *event));
-  event->data.scrollUpdate.deltaX += event_to_coalesce.data.scrollUpdate.deltaX;
-  event->data.scrollUpdate.deltaY += event_to_coalesce.data.scrollUpdate.deltaY;
+  if (event->type == WebInputEvent::GestureScrollUpdate) {
+    event->data.scrollUpdate.deltaX +=
+        event_to_coalesce.data.scrollUpdate.deltaX;
+    event->data.scrollUpdate.deltaY +=
+        event_to_coalesce.data.scrollUpdate.deltaY;
+  } else if (event->type == WebInputEvent::GesturePinchUpdate) {
+    event->data.pinchUpdate.scale *= event_to_coalesce.data.pinchUpdate.scale;
+  }
 }
 
 struct WebInputEventSize {
   template <class EventType>
   bool Execute(WebInputEvent::Type /* type */, size_t* type_size) const {
     *type_size = sizeof(EventType);
     return true;
   }
 };
 
@@ skipping 165 matching lines @@
     case WebInputEvent::MouseLeave:
     case WebInputEvent::ContextMenu:
       return true;
     default:
       break;
   }
   return false;
 }
 
 }  // namespace content