Port more String and HashMap usages

sky/engine/tonic/dart_exception_factory.cc

Index: sky/engine/tonic/dart_exception_factory.cc
diff --git a/sky/engine/tonic/dart_exception_factory.cc b/sky/engine/tonic/dart_exception_factory.cc
index e439a45393cad0e5d3af5b42fedb5ecc60d850fa..e8c348588ca768bc7b770f9ff3e4ae7f80ff0dd6 100644
--- a/sky/engine/tonic/dart_exception_factory.cc
+++ b/sky/engine/tonic/dart_exception_factory.cc
@@ -6,7 +6,6 @@
 
 #include "sky/engine/tonic/dart_converter.h"
 #include "sky/engine/tonic/dart_builtin.h"
-#include "sky/engine/wtf/text/StringBuilder.h"
 
 namespace blink {
 
@@ -18,23 +17,23 @@ DartExceptionFactory::~DartExceptionFactory() {
 }
 
 Dart_Handle DartExceptionFactory::CreateNullArgumentException(int index) {
-  StringBuilder message;
-  message.appendLiteral("Argument ");
-  message.appendNumber(index);
-  message.appendLiteral(" cannot be null.");
-  return CreateException("ArgumentError", message.toString());
+  std::string message;
+  message.append("Argument ");
+  message.append(std::to_string(index));
+  message.append(" cannot be null.");

[abarth-chromium, 2015/07/15 20:42:52]

This is super inefficient.  Is there no StringBuilder equivalent for
std::string?

+  return CreateException("ArgumentError", message);
 }
 
-Dart_Handle DartExceptionFactory::CreateException(const String& class_name,
-                                                  const String& message) {
+Dart_Handle DartExceptionFactory::CreateException(const std::string& class_name,
+                                                  const std::string& message) {
   if (core_library_.is_empty()) {
     Dart_Handle library = DartBuiltin::LookupLibrary("dart:core");
     core_library_.Set(dart_state_, library);
   }
 
   Dart_Handle exception_class = Dart_GetType(
-      core_library_.value(), StringToDart(dart_state_, class_name), 0, 0);
-  Dart_Handle message_handle = StringToDart(dart_state_, message);
+      core_library_.value(), StdStringToDart(class_name), 0, 0);
+  Dart_Handle message_handle = StdStringToDart(message);
   return Dart_New(exception_class, Dart_EmptyString(), 1, &message_handle);
 }