IDL compiler: sync Python to r166698 (and add test case)

Python side to:
Move encryptedmedia module to oilpan
https://codereview.chromium.org/139173012

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/154133003

git-svn-id: svn://svn.chromium.org/blink/trunk@166812 bbb929c8-8fbe-4397-9dbb-9b2b20218538