Port more String and HashMap usages

sky/engine/tonic/dart_exception_factory.h

Index: sky/engine/tonic/dart_exception_factory.h
diff --git a/sky/engine/tonic/dart_exception_factory.h b/sky/engine/tonic/dart_exception_factory.h
index 155eeb5cc652b0b2db6dbb344242d692675a5344..ca803f8a1068fa34a67f781724db64b13d21581a 100644
--- a/sky/engine/tonic/dart_exception_factory.h
+++ b/sky/engine/tonic/dart_exception_factory.h
@@ -5,9 +5,10 @@
 #ifndef SKY_ENGINE_TONIC_DART_EXCEPTION_FACTORY_H_
 #define SKY_ENGINE_TONIC_DART_EXCEPTION_FACTORY_H_
 
+#include <string>
+
 #include "dart/runtime/include/dart_api.h"
 #include "sky/engine/tonic/dart_persistent_value.h"
-#include "sky/engine/wtf/text/WTFString.h"
 
 namespace blink {
 class DartState;
@@ -18,7 +19,8 @@ class DartExceptionFactory {
   ~DartExceptionFactory();
 
   Dart_Handle CreateNullArgumentException(int index);
-  Dart_Handle CreateException(const String& class_name, const String& message);
+  Dart_Handle CreateException(const std::string& class_name,
+                              const std::string& message);
 
  private:
   DartState* dart_state_;