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

chrome/browser/ui/panels/panel_drag_controller.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 "chrome/browser/ui/panels/panel_drag_controller.h"
 
 #include "base/logging.h"
 #include "chrome/browser/ui/panels/detached_panel_strip.h"
 #include "chrome/browser/ui/panels/docked_panel_strip.h"
 #include "chrome/browser/ui/panels/panel.h"
@@ skipping 18 matching lines @@
     const gfx::Point& mouse_location) const {
   return mouse_location.Subtract(offset_from_mouse_location_on_drag_start_);
 }
 
 void PanelDragController::StartDragging(Panel* panel,
                                         const gfx::Point& mouse_location) {
   DCHECK(!dragging_panel_);
 
   last_mouse_location_ = mouse_location;
   offset_from_mouse_location_on_drag_start_ =
-      mouse_location.Subtract(panel->GetBounds().origin());
+      mouse_location.DistanceFrom(panel->GetBounds().origin());
 
   dragging_panel_ = panel;
   dragging_panel_->SetPreviewMode(true);
 
   // Keep track of original strip and placement for the case that the drag is
   // cancelled.
   dragging_panel_original_strip_ = dragging_panel_->panel_strip();
   dragging_panel_original_strip_->SavePanelPlacement(dragging_panel_);
 
   dragging_panel_original_strip_->StartDraggingPanelWithinStrip(
@@ skipping 167 matching lines @@
   if (dragging_panel_ == panel) {
     // The saved placement is no longer needed.
     dragging_panel_original_strip_->DiscardSavedPanelPlacement();
 
     // Clear the dragging state.
     dragging_panel_->panel_strip()->ClearDraggingStateWhenPanelClosed();
 
     dragging_panel_ = NULL;
   }
 }