Add an interface for retrieving the value of unsigned 64-bit integers.

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index f0174669476ef8aac8dd3b3161e5167b7a9203fe..5be1c88419bb21acf2ad8aae0c608038875d7f0b 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -12,7 +12,7 @@ const char* DartUtils::kIdFieldName = "_id";
 int64_t DartUtils::GetIntegerValue(Dart_Handle value_obj) {
   ASSERT(Dart_IsInteger(value_obj));
   int64_t value = 0;
-  Dart_Handle result = Dart_IntegerValue(value_obj, &value);
+  Dart_Handle result = Dart_IntegerToInt64(value_obj, &value);
   ASSERT(!Dart_IsError(result));
   return value;
 }