'git apply' works on Git indexes, so it's not possible
to apply a patch to src/third_party/webrtc with cwd=src/third_party.
Instead, set the cwd to the correct dir and add an extra patch
level using the new flag in https://codereview.chromium.org/1988583002/

This essentially reverts https://codereview.chromium.org/1977373002/
+ sets the project path correctly to src/third_party/webrtc.

BUG=438952

Review-Url: https://codereview.chromium.org/1984993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300616 0039d316-1c4b-4281-b951-d872f2087c98