IDL compiler: Overloaded methods with callback interface arguments

One use:
RTCPeerConnection.idl: addIceCandidate()

BUG=239771
R=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/130423002

git-svn-id: svn://svn.chromium.org/blink/trunk@164734 bbb929c8-8fbe-4397-9dbb-9b2b20218538