Update worker mode to use the bazel protos directly instead of json

DEPS

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
   # simply sdk, but if using special gclient specs it can be different.
   "dart_root": "sdk",
 
   # We use mirrors of all github repos to guarantee reproducibility and
@@ skipping 53 matching lines @@
   "mime_rev": "@75890811d4af5af080351ba8a2853ad4c8df98dd",
   "mustache4dart_rev" : "@5724cfd85151e5b6b53ddcd3380daf188fe47f92",
   "oauth2_tag": "@1.0.0",
   "observe_rev": "@eee2b8ec34236fa46982575fbccff84f61202ac6",
   "observatory_pub_packages_rev": "@cf90eb9077177d3d6b3fd5e8289477c2385c026a",
   "package_config_rev": "@0.1.3",
   "path_tag": "@1.3.6",
   "ply_rev": "@604b32590ffad5cbb82e4afef1d305512d06ae93",
   "plugin_tag": "@0.1.0",
   "pool_tag": "@1.2.1",
+  "protobuf_tag": "@0.5.0+1",
   "pub_rev": "@c1405b945c6d818c8cfe78334e8d4b11fd913103",
   "pub_cache_tag": "@v0.1.0",
   "pub_semver_tag": "@1.2.1",
   "quiver_tag": "@0.21.4",
   "resource_rev":"@a49101ba2deb29c728acba6fb86000a8f730f4b1",
   "root_certificates_rev": "@aed07942ce98507d2be28cbd29e879525410c7fc",
   "scheduled_test_tag": "@0.12.5+2",
   "shelf_tag": "@0.6.5",
   "smoke_rev" : "@f3361191cc2a85ebc1e4d4c33aec672d7915aba9",
   "source_maps_tag": "@0.10.1",
@@ skipping 134 matching lines @@
       + Var("observatory_pub_packages_rev"),
   Var("dart_root") + "/third_party/pkg_tested/package_config":
       (Var("github_mirror") % "package_config") +
       Var("package_config_rev"),
   Var("dart_root") + "/third_party/pkg/path":
       (Var("github_mirror") % "path") + Var("path_tag"),
   Var("dart_root") + "/third_party/pkg/plugin":
       (Var("github_mirror") % "plugin") + Var("plugin_tag"),
   Var("dart_root") + "/third_party/pkg/pool":
       (Var("github_mirror") % "pool") + Var("pool_tag"),
+  Var("dart_root") + "/third_party/pkg/protobuf":
+      (Var("github_dartlang") % "dart-protobuf") + Var("protobuf_tag"),
   Var("dart_root") + "/third_party/pkg/pub_semver":
       (Var("github_mirror") % "pub_semver") + Var("pub_semver_tag"),
   Var("dart_root") + "/third_party/pkg/pub":
       (Var("github_mirror") % "pub") + Var("pub_rev"),
   Var("dart_root") + "/third_party/pkg/pub_cache":
       (Var("github_mirror") % "pub_cache") + Var("pub_cache_tag"),
   Var("dart_root") + "/third_party/pkg/quiver":
       Var("chromium_git")
       + "/external/github.com/google/quiver-dart.git"
       + Var("quiver_tag"),
@@ skipping 203 matching lines @@
       "--extract",
       "-s",
       Var('dart_root') + "/third_party/clang.tar.gz.sha1",
     ],
   },
   {
     "pattern": ".",
     "action": ["python", Var("dart_root") + "/tools/gyp_dart.py"],
   },
 ]