IDL compiler: [SetReference]

New extended attribute, Python side to:
Reland: Reland: Implement new Blink IDL attribute [SetReference]
https://codereview.chromium.org/26792002

* Needed minor parser changes b/c using arguments:
[SetReference(A a, B b)]
* Also some test refactoring due to conflicting extended attributes.

BUG=239771
BUG=307341
R=haraken, kouhei
NOTRY=true

Review URL: https://codereview.chromium.org/114813006

git-svn-id: svn://svn.chromium.org/blink/trunk@164045 bbb929c8-8fbe-4397-9dbb-9b2b20218538