- Add an isolate field to visitors.

runtime/vm/gc_marker.cc

Index: runtime/vm/gc_marker.cc
===================================================================
--- runtime/vm/gc_marker.cc	(revision 8203)
+++ runtime/vm/gc_marker.cc	(working copy)
@@ -116,8 +116,12 @@
 
 class MarkingVisitor : public ObjectPointerVisitor {
  public:
-  MarkingVisitor(Heap* heap, PageSpace* page_space, MarkingStack* marking_stack)
-      : heap_(heap),
+  MarkingVisitor(Isolate* isolate,
+                 Heap* heap,
+                 PageSpace* page_space,
+                 MarkingStack* marking_stack)
+      : ObjectPointerVisitor(isolate),
+        heap_(heap),
         vm_heap_(Dart::vm_isolate()->heap()),
         page_space_(page_space),
         marking_stack_(marking_stack) {
@@ -314,7 +318,7 @@
                            bool invoke_api_callbacks) {
   MarkingStack marking_stack;
   Prologue(isolate, invoke_api_callbacks);
-  MarkingVisitor mark(heap_, page_space, &marking_stack);
+  MarkingVisitor mark(isolate, heap_, page_space, &marking_stack);
   IterateRoots(isolate, &mark, !invoke_api_callbacks);
   DrainMarkingStack(isolate, &mark);
   IterateWeakReferences(isolate, &mark);