check-webkit-style does not understand Obj-C literal syntax for NSDictionary

check-webkit-style does not understand Obj-C literal syntax for NSDictionary
<http://webkit.org/b/134061>

Reviewed by Dan Bernstein.

* Scripts/webkitpy/style/checkers/cpp.py:
(check_spacing): Ignore '@' immediately before '{'.
* Scripts/webkitpy/style/checkers/cpp_unittest.py:
(CppStyleTest.test_spacing_before_braces): Add unit test for
'^{' block syntax and '@{' Objective-C liternal NSDitionary
syntax.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@170152 268f45cc-cd09-0410-ab3c-d52691b4dbfc