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

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 6299afce2626eb886e23d1ce2042a56100a7327b..4789a873f49f59d9dff4a2b1e9448fbabe33c31f 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -602,7 +602,22 @@ DART_EXPORT Dart_Handle Dart_NewIntegerFromHexCString(const char* value);
  *
  * \return A valid handle if no error occurs during the operation.
  */
-DART_EXPORT Dart_Handle Dart_IntegerValue(Dart_Handle integer, int64_t* value);
+DART_EXPORT Dart_Handle Dart_IntegerToInt64(Dart_Handle integer,
+                                            int64_t* value);
+
+/**
+ * Gets the value of an Integer.
+ *
+ * The integer must fit into a 64-bit unsigned integer, otherwise an
+ * error occurs.
+ *
+ * \param integer An Integer.
+ * \param value Returns the value of the Integer.
+ *
+ * \return A valid handle if no error occurs during the operation.
+ */
+DART_EXPORT Dart_Handle Dart_IntegerToUint64(Dart_Handle integer,
+                                             uint64_t* value);
 
 /**
  * Gets the value of an integer as a hexadecimal C string.