Add support for WebRTC patches to Chromium trybots

Test case being added in https://codereview.chromium.org/1984623002/

NOTICE:
* Only patches from the webrtc/ subdirectory in a standalone
WebRTC checkout will work, since the root is set to src/third_party.
This can be changed once http://crbug.com/611808 is fixed. 
* The Chromium checkout will be synced to the DEPS-pinned revision
of WebRTC. Changing this to HEAD will be addressed in a future CL.
BUG=438952

Review-Url: https://codereview.chromium.org/1976243002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300588 0039d316-1c4b-4281-b951-d872f2087c98

recipe_modules/gclient/config.py

@@ -172,6 +172,9 @@ def chromium_bare(c):
   p['pdfium'] = ('src/third_party/pdfium', 'HEAD')
   p['skia'] = ('src/third_party/skia', 'HEAD')
   p['flac'] = ('src/third_party/flac', 'HEAD')
+  # TODO(kjellander): Change to the path below to src/third_party/webrtc mapping
+  # to 'HEAD' after http://crbug.com/611808 is fixed.
+  p['webrtc'] = ('src/third_party', None)
 
 @config_ctx(includes=['chromium_bare'])
 def chromium_empty(c):