Fix missing symbols error in OffscreenCanvas.o

third_party/WebKit/Source/core/offscreencanvas/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("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("offscreencanvas") {
   sources = [
     "OffscreenCanvas.cpp",
     "OffscreenCanvas.h",
   ]
+  deps = [
+    "//mojo/public/cpp/bindings:bindings",
+    "//third_party/WebKit/public:offscreen_canvas_mojo_bindings_blink",
+  ]
 }