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

ui/events/gesture_event_details.h

Index: ui/events/gesture_event_details.h
diff --git a/ui/events/gesture_event_details.h b/ui/events/gesture_event_details.h
index 377c4232c991e3c0d580002421667ce311b69bfa..2e4df3c03abc66cb3ccea5cf626201342fe8b5cc 100644
--- a/ui/events/gesture_event_details.h
+++ b/ui/events/gesture_event_details.h
@@ -17,9 +17,13 @@ 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|.
@@ -58,6 +62,11 @@ struct EVENTS_BASE_EXPORT GestureEventDetails {
     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;
@@ -68,6 +77,11 @@ struct EVENTS_BASE_EXPORT GestureEventDetails {
     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;
@@ -162,11 +176,13 @@ struct EVENTS_BASE_EXPORT GestureEventDetails {
       // 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;