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

ash/display/multi_display_manager.cc

Index: ash/display/multi_display_manager.cc
diff --git a/ash/display/multi_display_manager.cc b/ash/display/multi_display_manager.cc
index 3fc4ea54d82bbed9aef7a6dc5110c75ea4741826..fd7252fcb54a1bbf202d83ca1c4031f2651fd3fa 100644
--- a/ash/display/multi_display_manager.cc
+++ b/ash/display/multi_display_manager.cc
@@ -514,11 +514,11 @@ void MultiDisplayManager::EnsurePointerInDisplays() {
       break;
     }
     gfx::Point center = display_bounds.CenterPoint();
-    gfx::Point diff = center.Subtract(location_in_screen);
+    gfx::Vector2d diff = center.Subtract(location_in_screen);
     // Use the distance 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();
+    int64 distance = diff.LengthSquared();
     if (closest_distance < 0 || closest_distance > distance) {
       target_location = center;
       closest_distance = distance;