Get rid of deprecated methods accessing mutator_thread_ instead of current thread

runtime/vm/object_graph.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 "vm/object_graph.h"
 
 #include "vm/dart.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 138 matching lines @@
   static void UnmarkAll(Isolate* isolate) {
     Unmarker unmarker(isolate);
     isolate->heap()->IterateObjects(&unmarker);
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Unmarker);
 };
 
 
-ObjectGraph::ObjectGraph(Isolate* isolate)
-    : StackResource(isolate) {
+ObjectGraph::ObjectGraph(Thread* thread)
+    : StackResource(thread) {
   // The VM isolate has all its objects pre-marked, so iterating over it
   // would be a no-op.
-  ASSERT(isolate != Dart::vm_isolate());
-  isolate->heap()->WriteProtectCode(false);
+  ASSERT(thread->isolate() != Dart::vm_isolate());
+  thread->isolate()->heap()->WriteProtectCode(false);
 }
 
 
 ObjectGraph::~ObjectGraph() {
   isolate()->heap()->WriteProtectCode(true);
 }
 
 
 void ObjectGraph::IterateObjects(ObjectGraph::Visitor* visitor) {
   NoSafepointScope no_safepoint_scope_;
@@ skipping 299 matching lines @@
   {
     WritePointerVisitor ptr_writer(isolate(), stream);
     isolate()->IterateObjectPointers(&ptr_writer, false, false);
   }
   stream->WriteUnsigned(0);
   IterateObjects(&visitor);
   return visitor.count() + 1;  // + root
 }
 
 }  // namespace dart