Add helpers for logging mojom objects.

mojo/public/cpp/bindings/string.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_STRING_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_STRING_H_
 
+#include <iosfwd>
 #include <string>
 
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 #include "mojo/public/cpp/bindings/type_converter.h"
 #include "mojo/public/cpp/environment/logging.h"
 
 namespace mojo {
 
 // A UTF-8 encoded character string that can be null. Provides functions that
 // are similar to std::string, along with access to the underlying std::string
@@ skipping 97 matching lines @@
 inline bool operator!=(const String& a, const String& b) {
   return !(a == b);
 }
 inline bool operator!=(const char* a, const String& b) {
   return !(a == b);
 }
 inline bool operator!=(const String& a, const char* b) {
   return !(a == b);
 }
 
+// TODO(jeffbrown): Decide whether this should print a sentinel value
+// such as "<null>" when formatting null strings.
 inline std::ostream& operator<<(std::ostream& out, const String& s) {
   return out << s.get();
 }
 
 inline bool operator<(const String& a, const String& b) {
   if (a.is_null())
     return !b.is_null();
   if (b.is_null())
     return false;
 
@@ skipping 31 matching lines @@
 
 template <>
 struct TypeConverter<String, const char*> {
   // |input| may be null, in which case a null String will be returned.
   static String Convert(const char* input) { return String(input); }
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRING_H_