MacViews: Implement Tab Dragging

ui/gfx/geometry/rect.h

Index: ui/gfx/geometry/rect.h
diff --git a/ui/gfx/geometry/rect.h b/ui/gfx/geometry/rect.h
index a01e719882df5c6e2d6a150cde7619052f0cfbc6..6f7b296d39d54d317bd5f305bdf65434ef34b644 100644
--- a/ui/gfx/geometry/rect.h
+++ b/ui/gfx/geometry/rect.h
@@ -270,6 +270,10 @@ inline Rect ScaleToEnclosedRect(const Rect& rect, float scale) {
   return ScaleToEnclosedRect(rect, scale, scale);
 }
 
+// Will make the |p| fit inside |rect|, along the ledge that was closest to its
+// original position.
+GFX_EXPORT Point ConstrainToEnclosingRect(const Rect& rect, const Point& p);
+
 // This is declared here for use in gtest-based unit tests but is defined in
 // the gfx_test_support target. Depend on that to use this in your unit test.
 // This should not be used in production code - call ToString() instead.