clang-format: Initial (incomplete) support for the WebKit coding style.

This is far from implementing all the rules given by
http://www.webkit.org/coding/coding-style.html

The important new feature is the support for styles that don't have a
column limit. For such styles, clang-format will (at the moment) simply
respect the input's formatting decisions within statements.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187033 91177308-0d34-0410-b5e6-96231b3b80d8