Add patch file support to Dart embedder

mojo/dart/embedder/dart_controller.cc

 // Copyright 2014 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.
 
 #include "base/callback.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/path_service.h"
 #include "base/sys_info.h"
 #include "crypto/random.h"
@@ skipping 207 matching lines @@
 
   // Set up package root.
   result = Dart_NewStringFromUTF8(
       reinterpret_cast<const uint8_t*>(package_root.c_str()),
       package_root.length());
   DART_CHECK_VALID(result);
 
   const int kNumArgs = 1;
   Dart_Handle dart_args[kNumArgs];
   dart_args[0] = result;
-  return Dart_Invoke(builtin_lib,
+  result = Dart_Invoke(builtin_lib,
                      Dart_NewStringFromCString("_setPackageRoot"),
                      kNumArgs,
                      dart_args);
-
+  DART_CHECK_VALID(result);
   return result;
 }
 
 static Dart_Isolate CreateServiceIsolateHelper(const char* script_uri,
                                                char** error) {
   // TODO(johnmccutchan): Add support the service isolate.
   // No callbacks for service isolate.
   IsolateCallbacks callbacks;
   IsolateData* isolate_data =
       new IsolateData(NULL, false, callbacks, "", "", "");
@@ skipping 450 matching lines @@
 
   Dart_ExitScope();
   Dart_ShutdownIsolate();
   Dart_Cleanup();
   root_isolate_ = nullptr;
   initialized_ = false;
 }
 
 }  // namespace apps
 }  // namespace mojo