Remove unnecessary isolate argument from some visitors

runtime/vm/scavenger_test.cc

 // Copyright (c) 2014, 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 "platform/assert.h"
 #include "vm/scavenger.h"
 #include "vm/unit_test.h"
 #include "vm/visitor.h"
 
 namespace dart {
 
 // Expects to visit no objects (since the space should be empty).
 class FailingObjectVisitor : public ObjectVisitor {
  public:
-  FailingObjectVisitor() : ObjectVisitor(NULL) {}
+  FailingObjectVisitor() { }
   virtual void VisitObject(RawObject* obj) {
     EXPECT(false);
   }
 };
 
 // Expects to visit no objects (since the space should be empty).
 class FailingObjectPointerVisitor : public ObjectPointerVisitor {
  public:
   FailingObjectPointerVisitor() : ObjectPointerVisitor(NULL) {}
   virtual void VisitPointers(RawObject** first, RawObject** last) {
     EXPECT(false);
   }
 };
 
 // Expects to visit no objects (since the space should be empty).
 class FailingFindObjectVisitor : public FindObjectVisitor {
  public:
-  FailingFindObjectVisitor() : FindObjectVisitor(NULL) {}
+  FailingFindObjectVisitor() { }
   virtual bool FindObject(RawObject* obj) const {
     EXPECT(false);
     return false;
   }
 };
 
 TEST_CASE(ZeroSizeScavenger) {
   Scavenger* scavenger = new Scavenger(NULL, 0, kNewObjectAlignmentOffset);
   EXPECT(!scavenger->Contains(reinterpret_cast<uword>(&scavenger)));
   EXPECT_EQ(0, scavenger->UsedInWords());
   EXPECT_EQ(0, scavenger->CapacityInWords());
   EXPECT_EQ(static_cast<uword>(0), scavenger->TryAllocate(kObjectAlignment));
   FailingObjectVisitor obj_visitor;
   scavenger->VisitObjects(&obj_visitor);
   FailingObjectPointerVisitor ptr_visitor;
   scavenger->VisitObjectPointers(&ptr_visitor);
   FailingFindObjectVisitor find_visitor;
   scavenger->FindObject(&find_visitor);
   delete scavenger;
 }
 
 }  // namespace dart