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

[Evan Stade, 2016/12/01 02:39:02]

does this make sense? This API was a bit of a head scratcher for me and it's
pretty hard to debug when you can't figure out what the rect is supposed to be.

In fact, I'm not sure why we even need SetBorder. It seems like it's redundant
once you know the occlusion and the aperture.

In fact^2, it seems like aperture and layer bounds should be enough. Why do we
even need occlusion? Seems like we should just assume the outer edges of the
ninebox align to the edges of the layer's bounds.

+  // 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