[clang-format] Consider tok::hashhash in python-style comments

Summary: We were missing the case when python-style comments in text protos start with `##`.

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D47870

llvm-svn: 334179
diff --git a/clang/lib/Format/BreakableToken.cpp b/clang/lib/Format/BreakableToken.cpp
index 933dce3..f727f8d 100644
--- a/clang/lib/Format/BreakableToken.cpp
+++ b/clang/lib/Format/BreakableToken.cpp
@@ -44,7 +44,8 @@
                                             const FormatStyle &Style) {
   static const char *const KnownCStylePrefixes[] = {"///<", "//!<", "///", "//",
                                                     "//!"};
-  static const char *const KnownTextProtoPrefixes[] = {"//", "#"};
+  static const char *const KnownTextProtoPrefixes[] = {"//", "#", "##", "###",
+                                                       "####"};
   ArrayRef<const char *> KnownPrefixes(KnownCStylePrefixes);
   if (Style.Language == FormatStyle::LK_TextProto)
     KnownPrefixes = KnownTextProtoPrefixes;