check-webkit-style: do not warn about missing primary header for *SoftLink.cpp files

check-webkit-style: do not warn about missing primary header for *SoftLink.cpp files
<http://webkit.org/b/141799>

Reviewed by Alex Christensen.

* Scripts/webkitpy/style/checkers/cpp.py:
(_IncludeState.check_next_include_order): Don't emit a warning
if the primary header exists and the source file name ends with
"SoftLink.cpp".  Add 'filename' argument to method.
(check_include_line): Pass in 'filename'.

* Scripts/webkitpy/style/checkers/cpp_unittest.py:
(OrderOfIncludesTest.test_check_next_include_order__no_config):
(OrderOfIncludesTest.test_check_next_include_order__no_self):
(OrderOfIncludesTest.test_check_next_include_order__likely_then_config):
(OrderOfIncludesTest.test_check_next_include_order__other_then_config):
(OrderOfIncludesTest.test_check_next_include_order__config_then_other_then_likely):
- Add test filename arguments for calls to
  check_next_include_order().
(OrderOfIncludesTest.test_primary_header): Add test for a file
name ending in "SoftLink.cpp".

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@180355 268f45cc-cd09-0410-ab3c-d52691b4dbfc