IDL compiler: Test fix for partial interfaces, minor cleanup to compute_dependencies.py

Now that TestPartialInterfacePython2.idl is correctly being picked up,
there's a test failure due to a bug in the Perl CG
(handling of static members in a partial interface with [PerContextEnabled]).

I've thus commented out the test:
* This doesn't happen in practice, and
* there's only one use of [PerContextEnabled] on a partial interface,
core/page/WindowPagePopup.idl
which has one readonly attribute as a member.

Also cleanup of compute_dependencies.py: simplify one function call,
which also removes an incorrect naming (calling a basename the
interface_name when it might not be).

partial interfaces and implements are now done and tested;
still have inherited extended attributes and [PutForwards],
then dependencies are done in the compiler!

BUG=239771
TBR=haraken

Review URL: https://codereview.chromium.org/141653006

git-svn-id: svn://svn.chromium.org/blink/trunk@165503 bbb929c8-8fbe-4397-9dbb-9b2b20218538