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

chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc

Index: chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc
diff --git a/chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc b/chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc
index a785d9d3d505a8b8fd10305b0d277614afc7afc3..a10b0fdcc359068d3336ef485c603c9c8d366bb6 100644
--- a/chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc
+++ b/chrome/browser/ui/gtk/tabs/tab_renderer_gtk.cc
@@ -93,14 +93,14 @@ const int kCloseButtonHorzFuzz = 4;
 // Gets the bounds of |widget| relative to |parent|.
 gfx::Rect GetWidgetBoundsRelativeToParent(GtkWidget* parent,
                                           GtkWidget* widget) {
-  gfx::Point parent_pos = ui::GetWidgetScreenPosition(parent);
-  gfx::Point widget_pos = ui::GetWidgetScreenPosition(widget);
+  gfx::Vector2d parent_offset = ui::GetWidgetScreenOffset(parent);
+  gfx::Vector2d widget_offset = ui::GetWidgetScreenOffset(widget);
+  gfx::Vector2d relative_offset = widget_offset - parent_offset;
 
   GtkAllocation allocation;
   gtk_widget_get_allocation(widget, &allocation);
 
-  return gfx::Rect(widget_pos.x() - parent_pos.x(),
-                   widget_pos.y() - parent_pos.y(),
+  return gfx::Rect(relative_offset.x(), relative_offset.y(),
                    allocation.width, allocation.height);
 }