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

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
@@ skipping 3607 matching lines @@
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   const String& cls_name = Api::UnwrapStringHandle(isolate, name);
   if (cls_name.IsNull()) {
     RETURN_TYPE_ERROR(isolate, name, String);
   }
   const Library& lib = Api::UnwrapLibraryHandle(isolate, library);
   if (lib.IsNull()) {
     RETURN_TYPE_ERROR(isolate, library, Library);
   }
-  if (field_count <= 0) {
+  if (!Utils::IsUint(16, field_count)) {
     return Api::NewError(
-        "Negative field_count passed to Dart_CreateNativeWrapperClass");
+        "Invalid field_count passed to Dart_CreateNativeWrapperClass");
   }
   CHECK_CALLBACK_STATE(isolate);
 
   String& cls_symbol = String::Handle(isolate, Symbols::New(cls_name));
   const Class& cls = Class::Handle(
       isolate, Class::NewNativeWrapper(lib, cls_symbol, field_count));
   if (cls.IsNull()) {
     return Api::NewError(
         "Unable to create native wrapper class : already exists");
   }
@@ skipping 795 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart