Remove unnecessary isolate argument from some visitors

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 "lib/stacktrace.h"
@@ skipping 79 matching lines @@
 #define API_TIMELINE_BEGIN_END do { } while (false)
 #endif  // !PRODUCT
 
 #if defined(DEBUG)
 // An object visitor which will iterate over all the function objects in the
 // heap and check if the result type and parameter types are canonicalized
 // or not. An assertion is raised if a type is not canonicalized.
 class FunctionVisitor : public ObjectVisitor {
  public:
   explicit FunctionVisitor(Thread* thread) :
-      ObjectVisitor(thread->isolate()),
       classHandle_(Class::Handle(thread->zone())),
       funcHandle_(Function::Handle(thread->zone())),
       typeHandle_(AbstractType::Handle(thread->zone())) {}
 
   void VisitObject(RawObject* obj) {
     if (obj->IsFunction()) {
       funcHandle_ ^= obj;
       classHandle_ ^= funcHandle_.Owner();
       // Verify that the result type of a function is canonical or a
       // TypeParameter.
@@ skipping 6088 matching lines @@
   return Api::Success();
 }
 #endif  // DART_PRECOMPILER
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode() {
   return Dart::IsRunningPrecompiledCode();
 }
 
 }  // namespace dart