Add Dart_Allocate to the C++ API

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 c9d95be944ed62ff359f190166862e81d203ee56..f5fd33ab2cf3358db920fa1a35c6e31399b34f89 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -1753,6 +1753,16 @@ DART_EXPORT Dart_Handle Dart_New(Dart_Handle clazz,
                                  Dart_Handle* arguments);
 
 /**
+ * Allocate a new object without invoking a constructor.
+ *
+ * \param type The type of an object to be allocated.
+ *
+ * \return The new object. If an error occurs during execution, then an
+ *   error handle is returned.
+ */
+DART_EXPORT Dart_Handle Dart_Allocate(Dart_Handle type);
+
+/**
  * Invokes a method or function.
  *
  * The 'target' parameter may be an object, class, or library.  If