Add Vector2d classes that represent offsets, instead of using Point.

ui/app_list/apps_grid_view.cc

 // Copyright (c) 2012 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.
 
 #include "ui/app_list/apps_grid_view.h"
 
 #include <algorithm>
 
 #include "ui/app_list/app_list_item_model.h"
 #include "ui/app_list/app_list_item_view.h"
@@ skipping 151 matching lines @@
     pagination_model_->SelectPage(index.page, false);
 }
 
 void AppsGridView::InitiateDrag(views::View* view,
                                 Pointer pointer,
                                 const ui::LocatedEvent& event) {
   if (drag_view_)
     return;
 
   drag_view_ = view;
-  drag_offset_ = event.location();
+  drag_start_ = event.location();
 }
 
 void AppsGridView::UpdateDrag(views::View* view,
                               Pointer pointer,
                               const ui::LocatedEvent& event) {
   if (!dragging() && drag_view_ &&
-      ExceededDragThreshold(event.x() - drag_offset_.x(),
-                            event.y() - drag_offset_.y())) {
+      ExceededDragThreshold(event.location() - drag_start_)) {
     drag_pointer_ = pointer;
     // Move the view to the front so that it appears on top of other views.
     ReorderChildView(drag_view_, -1);
     bounds_animator_.StopAnimatingView(drag_view_);
   }
   if (drag_pointer_ == pointer) {
     last_drag_point_ = event.location();
     views::View::ConvertPointToTarget(drag_view_, this, &last_drag_point_);
 
     const Index last_drop_target = drop_target_;
     CalculateDropTarget(last_drag_point_);
     MaybeStartPageFlipTimer(last_drag_point_);
 
     gfx::Point page_switcher_point(last_drag_point_);
     views::View::ConvertPointToTarget(this, page_switcher_view_,
                                       &page_switcher_point);
     page_switcher_view_->UpdateUIForDragPoint(page_switcher_point);
 
     if (last_drop_target != drop_target_)
       AnimateToIdealBounds();
-    drag_view_->SetPosition(last_drag_point_.Subtract(drag_offset_));
+    drag_view_->SetPosition(
+        gfx::PointAtOffsetFromOrigin(last_drag_point_ - drag_start_));
   }
 }
 
 void AppsGridView::EndDrag(bool cancel) {
   if (!cancel && dragging() && drag_view_ && IsValidIndex(drop_target_))
     MoveItemInModel(drag_view_, drop_target_);
 
   drag_pointer_ = NONE;
   drop_target_ = Index();
   if (drag_view_) {
@@ skipping 486 matching lines @@
 void AppsGridView::TransitionChanged() {
   // Update layout for valid page transition only since over-scroll no longer
   // animates app icons.
   const PaginationModel::Transition& transition =
       pagination_model_->transition();
   if (pagination_model_->is_valid_page(transition.target_page))
     Layout();
 }
 
 }  // namespace app_list