Add SkBitmap StructTraits for skia::mojo::Bitmap.

mash/shelf/public/interfaces/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "shelf.mojom",
     "shelf_constants.mojom",
   ]
 
-  deps = [
+  public_deps = [
     "//skia/public/interfaces",
   ]
 }