webkitpy: test_function_length_check_definition_huge_lines is slow

webkitpy: test_function_length_check_definition_huge_lines is slow
https://bugs.webkit.org/show_bug.cgi?id=79185

Reviewed by Adam Barth.

This test takes ~3 seconds to run, apparently because we're
running a test on a 10,000 line function :). Dropping the
function length to 640 still exercises the code path and
provides a 10x speedup.

* Scripts/webkitpy/style/checkers/cpp_unittest.py:
(CppStyleTest):
(CheckForFunctionLengthsTest.test_function_length_check_definition_huge_lines):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108515 268f45cc-cd09-0410-ab3c-d52691b4dbfc