Pull Chromium dependencies to Pipa checkout via DEPS and GITDEPS.

GITDEPS

+# Copyright 2015 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# This file is read by gitdeps.py to allow loading subsections of git repos
+# through sparse checkouts.
+
+vars = {
+  "chrome_revision": "a691a7278a6f58da832b8818d2d00afa0687cd0d",
+  "gyp_revision": "bac4680ec9a5c55ab692490b6732999648ecf1e9",
+  "chrome_base_git": "https://chromium.googlesource.com/",
+}
+
+deps = {
+  "":(
+    Var("chrome_base_git") + "chromium/src",
+    [
+      # Chrome base and other top-level dependencies.
+      "base",
+      "build",
+      "testing",
+      "tools",
+
+      # third_party dependencies.
+      "third_party/protobuf",
+    ],
+    Var("chrome_revision")
+  ),
+  "tools/gyp":
+    (Var("chrome_base_git") + "external/gyp/",
+    [],
+    Var("gyp_revision")),
+}