Add a .clang-format file to give us local control over Chromium style.

This also makes editor integration somewhat easier by letting editors pass just
"-style=file -assume-filename=<filename>" to clang-format instead of needing to
guess the desired style based on the path.

We could name this file _clang-format instead, if that's easier for Windows.

Review URL: https://codereview.chromium.org/52093012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232271 0039d316-1c4b-4281-b951-d872f2087c98

.clang-format

@@ -0,0 +1,3 @@
+# Defines the Chromium style for automatic reformatting.
+# http://clang.llvm.org/docs/ClangFormatStyleOptions.html
+BasedOnStyle: Chromium