Add JSON-specific escaping, which has different rules from JS escaping.

base/string_util.h

Index: base/string_util.h
===================================================================
--- base/string_util.h	(revision 16481)
+++ base/string_util.h	(working copy)
@@ -595,5 +595,33 @@
 //   std::numeric_limits<size_t>::max() / 2
 std::string HexEncode(const void* bytes, size_t size);
 
+// Hack to convert any char-like type to its unsigned counterpart.
+// For example, it will convert char, signed char and unsigned char to unsigned
+// char.
+template<typename T>
+struct ToUnsigned {
+  typedef T Unsigned;
+};
 
+template<>
+struct ToUnsigned<char> {
+  typedef unsigned char Unsigned;
+};
+template<>
+struct ToUnsigned<signed char> {
+  typedef unsigned char Unsigned;
+};
+template<>
+struct ToUnsigned<wchar_t> {
+#if defined(WCHAR_T_IS_UTF16)
+  typedef unsigned short Unsigned;
+#elif defined(WCHAR_T_IS_UTF32)
+  typedef uint32 Unsigned;
+#endif
+};
+template<>
+struct ToUnsigned<short> {
+  typedef unsigned short Unsigned;
+};
+
 #endif  // BASE_STRING_UTIL_H_