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

ash/display/multi_display_manager.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 "ash/display/multi_display_manager.h"
 
 #include <string>
 #include <vector>
 
 #include "ash/display/display_controller.h"
@@ skipping 494 matching lines @@
   *internal_display_ = displays_[0];
   return internal_display_id_;
 }
 
 void MultiDisplayManager::EnsurePointerInDisplays() {
   // Don't try to move the pointer during the boot/startup.
   if (!Shell::HasInstance())
     return;
   gfx::Point location_in_screen = Shell::GetScreen()->GetCursorScreenPoint();
   gfx::Point target_location;
-  int64 closest_distance = -1;
+  int64 closest_distance_squared = -1;
 
   for (DisplayList::const_iterator iter = displays_.begin();
        iter != displays_.end(); ++iter) {
     const gfx::Rect& display_bounds = iter->bounds();
 
     if (display_bounds.Contains(location_in_screen)) {
       target_location = location_in_screen;
       break;
     }
     gfx::Point center = display_bounds.CenterPoint();
-    gfx::Point diff = center.Subtract(location_in_screen);
-    // Use the distance from the center of the dislay. This is not
+    // Use the distance squared from the center of the dislay. This is not
     // exactly "closest" display, but good enough to pick one
     // appropriate (and there are at most two displays).
-    int64 distance = diff.x() * diff.x() + diff.y() * diff.y();
-    if (closest_distance < 0 || closest_distance > distance) {
+    // We don't care about actual distance, only relative to other displays, so
+    // using the LengthSquared() is cheaper than Length().
+    int64 distance_squared = (center - location_in_screen).LengthSquared();
+    if (closest_distance_squared < 0 ||
+        closest_distance_squared > distance_squared) {
       target_location = center;
-      closest_distance = distance;
+      closest_distance_squared = distance_squared;
     }
   }
 
   aura::RootWindow* root_window = Shell::GetPrimaryRootWindow();
   aura::client::ScreenPositionClient* client =
       aura::client::GetScreenPositionClient(root_window);
   client->ConvertPointFromScreen(root_window, &target_location);
 
   root_window->MoveCursorTo(target_location);
 }
 
 void MultiDisplayManager::SetDisplayIdsForTest(DisplayList* to_update) const {
   DisplayList::iterator iter_to_update = to_update->begin();
   DisplayList::const_iterator iter = displays_.begin();
   for (; iter != displays_.end() && iter_to_update != to_update->end();
        ++iter, ++iter_to_update) {
     (*iter_to_update).set_id((*iter).id());
   }
 }
 
 }  // namespace internal
 }  // namespace ash