Add clang-format configuration file and set coding style to "Google"

c.f. https://code.google.com/p/v8/wiki/Contributing

BUG=none
R=jkummerow@chromium.org, machenbach@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/80783004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17979 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

.clang-format

+# Defines the Google C++ style for automatic reformatting.
+# http://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: Google