gyp_chromium: Better parsing of -G command line flag.

build/PRESUBMIT.py

Index: build/PRESUBMIT.py
diff --git a/build/PRESUBMIT.py b/build/PRESUBMIT.py
new file mode 100644
index 0000000000000000000000000000000000000000..3c701930a97988175cfc5bf7828a768487e03332
--- /dev/null
+++ b/build/PRESUBMIT.py
@@ -0,0 +1,18 @@
+# Copyright 2015 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.
+
+WHITELIST = [ r'.+_test.py$' ]
+
+
+def _RunTests(input_api, output_api):
+  return (input_api.canned_checks.RunUnitTestsInDirectory(
+          input_api, output_api, '.', whitelist=[r'.+_test.py$']))
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _RunTests(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return _RunTests(input_api, output_api)