Remove unnecessary isolate argument from some visitors

runtime/vm/verifier.cc

 // Copyright (c) 2012, 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 "vm/verifier.h"
 
 #include "platform/assert.h"
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/freelist.h"
@@ skipping 24 matching lines @@
         break;
        case kRequireMarked:
         if (!raw_obj->IsMarked()) {
           FATAL1("Unmarked object encountered %#" Px "\n", raw_addr);
         }
         break;
       }
     }
   }
   allocated_set_->Add(raw_obj);
-  raw_obj->Validate(isolate());
+  raw_obj->Validate(isolate_);
 }
 
 
 void VerifyPointersVisitor::VisitPointers(RawObject** first, RawObject** last) {
   for (RawObject** current = first; current <= last; current++) {
     VerifiedMemory::Verify(reinterpret_cast<uword>(current), kWordSize);
     RawObject* raw_obj = *current;
     if (raw_obj->IsHeapObject()) {
       if (!allocated_set_->Contains(raw_obj)) {
         uword raw_addr = RawObject::ToAddr(raw_obj);
@@ skipping 21 matching lines @@
   // Visit all strongly reachable objects.
   isolate->IterateObjectPointers(&visitor,
                                  StackFrameIterator::kValidateFrames);
   VerifyWeakPointersVisitor weak_visitor(&visitor);
   // Visit weak handles and prologue weak handles.
   isolate->VisitWeakPersistentHandles(&weak_visitor);
   delete allocated_set;
 }
 
 }  // namespace dart