[DevTools] Add a fetch config for the inspector_protocol.

This will facilitate a more standalone development process.
We don't have a DEPS file there yet, but I'm planning
to add a simple one, which for starters will
have gunit. I'll model this mostly after breakpad.
I've tested this fetch config and it appears to work great:

$ mkdir testfetch
$ cd testfetch
$ fetch inspector_protocol

After this there's an src directory in testfetch which
has our sources.

Change-Id: I482d65b3d8e50e9e5a98c4affc7b487a5bd6df53
Reviewed-on: https://chromium-review.googlesource.com/c/1340502
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

fetch_configs/inspector_protocol.py

+# Copyright (c) 2018 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.
+
+import sys
+
+import config_util  # pylint: disable=import-error
+
+
+# This class doesn't need an __init__ method, so we disable the warning
+# pylint: disable=no-init
+class InspectorProtocol(config_util.Config):
+  @staticmethod
+  def fetch_spec(props):
+    url = 'https://chromium.googlesource.com/deps/inspector_protocol.git'
+    solution = {
+      'name': 'src',
+      'url': url,
+      'managed': False,
+      'custom_deps': {},
+    }
+    spec = {
+      'solutions': [solution],
+    }
+    return {
+      'type': 'gclient_git',
+      'gclient_git_spec': spec,
+    }
+
+  @staticmethod
+  def expected_root(_props):
+    return 'src'
+
+
+def main(argv=None):
+  return InspectorProtocol().handle_args(argv)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))