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

ash/tooltips/tooltip_controller.cc

Index: ash/tooltips/tooltip_controller.cc
diff --git a/ash/tooltips/tooltip_controller.cc b/ash/tooltips/tooltip_controller.cc
index 45c4785c081f034c93ce8c86c013bb5c6f1490fa..047975d538850ecb6fbf987d56b9ebeb7d1dbbc3 100644
--- a/ash/tooltips/tooltip_controller.cc
+++ b/ash/tooltips/tooltip_controller.cc
@@ -452,7 +452,7 @@ void TooltipController::UpdateIfRequired() {
       string16 tooltip_text(tooltip_text_);
       gfx::Point widget_loc = curr_mouse_loc_;

[Peter Kasting, 2012/10/27 01:01:39]

Nit: Inline both of these statements into the SetText() call

[danakj, 2012/10/29 19:17:20]

Done.

       widget_loc = widget_loc.Add(
-          tooltip_window_->GetBoundsInScreen().origin());
+          tooltip_window_->GetBoundsInScreen().OffsetFromOrigin());

[Peter Kasting, 2012/10/27 01:01:39]

Can we replace GetBoundsInScreen() with a function that returns a vector
directly?

[danakj, 2012/10/29 19:17:20]

I don't think we want to replace the method. There's a lot of callers of things
like:
GetBoundsInScreen().CenterPoint()
GetBoundsInScreen().Contains(...)
Intersects(GetBoundsInScreen())

We could add a method along side it, however. Shall we do that in this CL
though? It doesn't seem intrinsic to the change to me, since there are so many
callers of this, and there's no GetPositionInScreen() at the moment to convert.

       GetTooltip()->SetText(tooltip_text, widget_loc);
       GetTooltip()->Show();
       tooltip_shown_timer_.Start(FROM_HERE,