Track whether a scroll sequence has been partially prevented

ui/events/gesture_event_details.cc

Index: ui/events/gesture_event_details.cc
diff --git a/ui/events/gesture_event_details.cc b/ui/events/gesture_event_details.cc
index 780713118d348dfdd4e31814ae97b24385f818c6..e14fb17302ab12fd89050b62cd4a6e25c3f5423d 100644
--- a/ui/events/gesture_event_details.cc
+++ b/ui/events/gesture_event_details.cc
@@ -24,30 +24,30 @@ GestureEventDetails::GestureEventDetails(ui::EventType type,
   DCHECK_LE(type, ET_GESTURE_TYPE_END);
   switch (type_) {
     case ui::ET_GESTURE_SCROLL_BEGIN:
-      data.scroll_begin.x_hint = delta_x;
-      data.scroll_begin.y_hint = delta_y;
+      data_.scroll_begin.x_hint = delta_x;
+      data_.scroll_begin.y_hint = delta_y;
       break;
 
     case ui::ET_GESTURE_SCROLL_UPDATE:
-      data.scroll_update.x = delta_x;
-      data.scroll_update.y = delta_y;
+      data_.scroll_update.x = delta_x;
+      data_.scroll_update.y = delta_y;
       break;
 
     case ui::ET_SCROLL_FLING_START:
-      data.fling_velocity.x = delta_x;
-      data.fling_velocity.y = delta_y;
+      data_.fling_velocity.x = delta_x;
+      data_.fling_velocity.y = delta_y;
       break;
 
     case ui::ET_GESTURE_TWO_FINGER_TAP:
-      data.first_finger_enclosing_rectangle.width = delta_x;
-      data.first_finger_enclosing_rectangle.height = delta_y;
+      data_.first_finger_enclosing_rectangle.width = delta_x;
+      data_.first_finger_enclosing_rectangle.height = delta_y;
       break;
 
     case ui::ET_GESTURE_SWIPE:
-      data.swipe.left = delta_x < 0;
-      data.swipe.right = delta_x > 0;
-      data.swipe.up = delta_y < 0;
-      data.swipe.down = delta_y > 0;
+      data_.swipe.left = delta_x < 0;
+      data_.swipe.right = delta_x > 0;
+      data_.swipe.up = delta_y < 0;
+      data_.swipe.down = delta_y > 0;
       break;
 
     default:
@@ -55,6 +55,33 @@ GestureEventDetails::GestureEventDetails(ui::EventType type,
   }
 }
 
+GestureEventDetails::GestureEventDetails(ui::EventType type,
+                                         const GestureEventDetails& other)
+    : type_(type),
+      data_(other.data_),
+      touch_points_(other.touch_points_),
+      bounding_box_(other.bounding_box_),
+      oldest_touch_id_(other.oldest_touch_id_) {
+  DCHECK_GE(type, ET_GESTURE_TYPE_START);
+  DCHECK_LE(type, ET_GESTURE_TYPE_END);
+  switch (type) {
+    case ui::ET_GESTURE_SCROLL_BEGIN:
+      // Synthetic creation of SCROLL_BEGIN from PINCH_BEGIN is explicitly
+      // allowed as an exception.
+      if (other.type() == ui::ET_GESTURE_PINCH_BEGIN)
+        break;
+    case ui::ET_GESTURE_SCROLL_UPDATE:
+    case ui::ET_SCROLL_FLING_START:
+    case ui::ET_GESTURE_SWIPE:
+    case ui::ET_GESTURE_PINCH_UPDATE:
+      DCHECK_EQ(type, other.type()) << " - Invalid gesture conversion from "
+                                    << other.type() << " to " << type;
+      break;
+    default:
+      break;

[sadrul, 2014/11/18 17:53:45]

NOTREACHED()? Or no because the caller is responsible to ensure this?

[jdduke (slow), 2014/11/18 19:50:46]

For these cases, we don't really care about the source type as we're not using
the details union.

+  }
+}
+
 GestureEventDetails::Details::Details() {
   memset(this, 0, sizeof(Details));
 }