Route OnDragEvent through ViewAndroid tree

ui/events/android/motion_event_android.h

Index: ui/events/android/motion_event_android.h
diff --git a/ui/events/android/motion_event_android.h b/ui/events/android/motion_event_android.h
index 1411dc4fa730ee32071048aec64b9475bd352c63..a208366a6b5f13688afd18c410950ac8cf62b02a 100644
--- a/ui/events/android/motion_event_android.h
+++ b/ui/events/android/motion_event_android.h
@@ -68,7 +68,12 @@ class EVENTS_EXPORT MotionEventAndroid : public MotionEvent {
                      const Pointer* const pointer1);
   ~MotionEventAndroid() override;
 
-  std::unique_ptr<MotionEventAndroid> Offset(float x, float y) const;
+  // Create a new instance from |this| with its cached pointers set
+  // to a given point.
+  std::unique_ptr<MotionEventAndroid> CreateFor(const gfx::PointF& point) const;
+
+  // Convenience method returning the pointer at index 0.
+  gfx::PointF GetPoint() const { return gfx::PointF(GetX(0), GetY(0)); }
 
   // ui::MotionEvent methods.
   uint32_t GetUniqueEventId() const override;
@@ -113,9 +118,8 @@ class EVENTS_EXPORT MotionEventAndroid : public MotionEvent {
 
   float ToDips(float pixels) const;
   CachedPointer FromAndroidPointer(const Pointer& pointer) const;
-  CachedPointer OffsetCachedPointer(const CachedPointer& pointer,
-                                    float x,
-                                    float y) const;
+  CachedPointer CreateCachedPointer(const CachedPointer& pointer,
+                                    const gfx::PointF& point) const;
 
   // Cache pointer coords, id's and major lengths for the most common
   // touch-related scenarios, i.e., scrolling and pinching.  This prevents