Draw omnibox shadow with a ninebox layer.

cc/layers/nine_patch_layer.h

Index: cc/layers/nine_patch_layer.h
diff --git a/cc/layers/nine_patch_layer.h b/cc/layers/nine_patch_layer.h
index cf9edf99c72c9f6102c73746d82fd94e8cb95f33..e5cf11ca5f6bbe4817243f105ddfea444a4e7f59 100644
--- a/cc/layers/nine_patch_layer.h
+++ b/cc/layers/nine_patch_layer.h
@@ -27,6 +27,9 @@ class CC_EXPORT NinePatchLayer : public UIResourceLayer {
   // size of the left and top boundary, respectively.
   // |border.width()-border.x()| and |border.height()-border.y()| are the size
   // of the right and bottom boundary, respectively.
+  // TODO(estade): this really ought to be a gfx::Insets and not a gfx::Rect. To
+  // convert from rect to insets, think of x() as left(), y() as top(), width()
+  // - x() as right(), and height() - y() as bottom().
   void SetBorder(const gfx::Rect& border);
 
   // aperture is in the pixel space of the bitmap resource and refers to