idl_parser: Made unittests for Extended Attribute

In this CL I made 7 unittests for Extend Attribute definitions.
There are 5 main patterns for Extended Attribute
and I made tests for each ( 0) ~ 4) below ).
In addition to them, I made 1 test for a combination 
of 2 patterns of Extended Attributes (5)) and 1 error test(6)).

I don't think these tests for Extended Attribute are enough, 
and please tell me what kind of tests I should add.

detail of this CL:
 (tools/idl_parser/idl_parser_test.py:
   Line 176 ~ 323)
- 7 tests
 -0) testNoArguments
 -1) testArgumentList
 -2) testNamedArgumentList
 -3) testIdentifier
 -4) testIdentifierList
 -5) testCombinationOfExtendedAttributes
 -6) testErrorTrailingComma

- made slight changes of coding style in other tests

Bug: 617899
Change-Id: I97816867f3a2c645ac6359bbff71d7220c3e69e3
Reviewed-on: https://chromium-review.googlesource.com/620333
Commit-Queue: Lisa Suzuki <lisabelle@google.com>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#495902}
3 files changed