Break the class-inheritance ":" to the new line.

This seems to be more common in LLVM, Google and Chromium.

Before:
class AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA :
    public BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
    public CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC {
};

After:
class AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
    : public BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB,
      public CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC {
};