Cache number of type arguments in class object instead of recalculating it.

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
===================================================================
--- runtime/vm/stub_code_x64.cc	(revision 28669)
+++ runtime/vm/stub_code_x64.cc	(working copy)
@@ -1086,8 +1086,8 @@
   const intptr_t kObjectTypeArgumentsOffset = 2 * kWordSize;
   const intptr_t kInstantiatorTypeArgumentsOffset = 1 * kWordSize;
   // The generated code is different if the class is parameterized.
-  const bool is_cls_parameterized = cls.HasTypeArguments();
-  ASSERT(!cls.HasTypeArguments() ||
+  const bool is_cls_parameterized = cls.NumTypeArguments() > 0;
+  ASSERT(!is_cls_parameterized ||
          (cls.type_arguments_field_offset() != Class::kNoTypeArguments));
   // kInlineInstanceSize is a constant used as a threshold for determining
   // when the object initialization should be done as a loop or as
@@ -1260,7 +1260,7 @@
   const bool is_implicit_instance_closure =
       func.IsImplicitInstanceClosureFunction();
   const Class& cls = Class::ZoneHandle(func.signature_class());
-  const bool has_type_arguments = cls.HasTypeArguments();
+  const bool has_type_arguments = cls.NumTypeArguments() > 0;
 
   __ EnterStubFrameWithPP();  // Uses pool pointer to refer to function.
   __ LoadObject(R12, Object::null_object(), PP);