Fix mouse wheel over-scrolls when display is scaled and scroll is paginated

ui/events/gesture_event_details.h

 // Copyright 2014 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.
 
 #ifndef UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DETAILS_H_
 #define UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DETAILS_H_
 
 #include <string.h>
 
 #include "base/logging.h"
 #include "ui/events/event_constants.h"
 #include "ui/events/events_base_export.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 
 namespace ui {
 
 struct EVENTS_BASE_EXPORT GestureEventDetails {
  public:
+  enum ScrollUnits { PrecisePixels = 0, Pixels, Page };

[sky, 2017/02/17 18:00:25]

chrome style is ALL_CAPS. Also, use enum class.

Also, please document what these values mean. It isn't at all clear what
differentiates 'precise' from non-precise.

[chengx, 2017/02/17 20:52:46]

I copied this enum definition from WebGestureEvent.h in webKit, because
WebGestureEvent.h is not allowed to be included here. In more details, git cl
upload cannot be completed due to this style issue. 

Anyway, I have added comments, switched to ALL_CAPS and enum class.

   GestureEventDetails();
   explicit GestureEventDetails(EventType type);
-  GestureEventDetails(EventType type, float delta_x, float delta_y);
+  GestureEventDetails(EventType type,
+                      float delta_x,
+                      float delta_y,
+                      ScrollUnits units = PrecisePixels);
 
   // The caller is responsible for ensuring that the gesture data from |other|
   // is compatible and sufficient for that expected by gestures of |type|.
   GestureEventDetails(EventType type, const GestureEventDetails& other);
 
   EventType type() const { return type_; }
 
   GestureDeviceType device_type() const { return device_type_; }
   void set_device_type(GestureDeviceType device_type) {
     device_type_ = device_type;
@@ skipping 18 matching lines @@
   float scroll_x_hint() const {
     DCHECK_EQ(ET_GESTURE_SCROLL_BEGIN, type_);
     return data_.scroll_begin.x_hint;
   }
 
   float scroll_y_hint() const {
     DCHECK_EQ(ET_GESTURE_SCROLL_BEGIN, type_);
     return data_.scroll_begin.y_hint;
   }
 
+  ScrollUnits scroll_units_hint() const {

[sky, 2017/02/17 18:00:25]

scroll_begin_units?

[chengx, 2017/02/17 20:52:46]

Done.

+    DCHECK_EQ(ET_GESTURE_SCROLL_BEGIN, type_);
+    return data_.scroll_begin.deltaHintUnits;
+  }
+
   float scroll_x() const {
     DCHECK_EQ(ET_GESTURE_SCROLL_UPDATE, type_);
     return data_.scroll_update.x;
   }
 
   float scroll_y() const {
     DCHECK_EQ(ET_GESTURE_SCROLL_UPDATE, type_);
     return data_.scroll_update.y;
   }
 
+  ScrollUnits scroll_units() const {

[sky, 2017/02/17 18:00:25]

scroll_update_units?

[chengx, 2017/02/17 20:52:46]

Done.

+    DCHECK_EQ(ET_GESTURE_SCROLL_UPDATE, type_);
+    return data_.scroll_update.deltaUnits;
+  }
+
   float velocity_x() const {
     DCHECK_EQ(ET_SCROLL_FLING_START, type_);
     return data_.fling_velocity.x;
   }
 
   float velocity_y() const {
     DCHECK_EQ(ET_SCROLL_FLING_START, type_);
     return data_.fling_velocity.y;
   }
 
@@ skipping 74 matching lines @@
 
  private:
   EventType type_;
   union Details {
     Details();
     struct {  // SCROLL start details.
       // Distance that caused the scroll to start.  Generally redundant with
       // the x/y values from the first scroll_update.
       float x_hint;
       float y_hint;
+      ScrollUnits deltaHintUnits;

[sky, 2017/02/17 18:00:25]

delta_hint_units.

[chengx, 2017/02/17 20:52:46]

Done.

     } scroll_begin;
 
     struct {  // SCROLL delta.
       float x;
       float y;
+      ScrollUnits deltaUnits;

[sky, 2017/02/17 18:00:25]

delta_units.

[chengx, 2017/02/17 20:52:46]

Done.

       // Whether any previous scroll update in the current scroll sequence was
       // suppressed because the underlying touch was consumed.
       bool previous_update_in_sequence_prevented;
     } scroll_update;
 
     float scale;  // PINCH scale.
 
     struct {  // FLING velocity.
       float x;
       float y;
@@ skipping 23 matching lines @@
   int touch_points_;  // Number of active touch points in the gesture.
 
   // Bounding box is an axis-aligned rectangle that contains all the
   // enclosing rectangles of the touch-points in the gesture.
   gfx::RectF bounding_box_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_GESTURE_EVENT_DETAILS_H_