IDL compiler: sync Python to r166277

Python side to:
Pass an Isolate around in context related methods
https://codereview.chromium.org/151283002

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/134623010

git-svn-id: svn://svn.chromium.org/blink/trunk@166285 bbb929c8-8fbe-4397-9dbb-9b2b20218538