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:
+  // The definition of ScrollUnits below is consistent with that in
+  // //src/third_party/WebKit/public/platform/WebGestureEvent.h
+  enum class ScrollUnits {
+    PRECISE_PIXELS = 0,  // generated by high precision devices.
+    PIXELS,              // large pixel jump duration; should animate to delta.
+    PAGE                 // page (visible viewport) based scrolling.
+  };
+
   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 = ScrollUnits::PRECISE_PIXELS);

[Bret, 2017/02/17 21:06:03]

nit: add a short comment saying this is the default in WebGestureEvent too

[chengx, 2017/02/17 21:57:45]

Done.

 
   // 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_begin_units() const {
+    DCHECK_EQ(ET_GESTURE_SCROLL_BEGIN, type_);
+    return data_.scroll_begin.delta_hint_units;
+  }
+
   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_update_units() const {
+    DCHECK_EQ(ET_GESTURE_SCROLL_UPDATE, type_);
+    return data_.scroll_update.delta_units;
+  }
+
   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 delta_hint_units;
     } scroll_begin;
 
     struct {  // SCROLL delta.
       float x;
       float y;
+      ScrollUnits delta_units;
       // 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_