Fixed the following format errors:

webapi/resources/validate_diff.py:104:22: E201 whitespace after '('

webapi/resources/validate_diff.py:105:22: E128 continuation line under-indented for visual indent

webapi/resources/validate_diff.py:105:25: E201 whitespace after '('

webapi/resources/validate_diff.py:106:25: E128 continuation line under-indented for visual indent

webapi/resources/validate_diff.py:107:25: E128 continuation line under-indented for visual indent

webapi/tests/mixins.py:572:1: E303 too many blank lines (3)

webapi/tests/mixins.py:859:1: E303 too many blank lines (3)

webapi/tests/test_review_request_draft.py:61:5: E303 too many blank lines (2)

Ran unit tests, and pep8.