clang-format: [JS] Basic support for escape sequences in regex literals.

Before:
  var regex = /\\/ g; // This isn't even recognized as regex.

After:
  var regex = /\\/g; // It now is.

llvm-svn: 208539
diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
index cc67416..7a853b0 100644
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -180,6 +180,9 @@
   verifyFormat("var regex = /\\W/;");
   verifyFormat("var regex = /a(a)\\1/;");
   verifyFormat("var regex = /\\0/;");
+  verifyFormat("var regex = /\\\\/g;");
+  verifyFormat("var regex = /\\a\\\\/g;");
+  verifyFormat("var regex = /\a\\//g;");
 }
 
 TEST_F(FormatTestJS, RegexLiteralModifiers) {