Set the chromium_code GYP variable

build/crashpad.gypi

+# Copyright 2015 The Crashpad Authors. 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.
+
+{
+  'variables': {
+    # When building as a part of Chromium, this variable sets up the build to
+    # treat Crashpad as Chromium code. This enables warnings at an appropriate
+    # level and applies Chromium’s build/filename_rules.gypi. In a standalone
+    # build, this variable has no effect.
+    'chromium_code': 1,
+  },
+}