- Account for live size in marker.

runtime/vm/gc_marker.h

Index: runtime/vm/gc_marker.h
===================================================================
--- runtime/vm/gc_marker.h	(revision 35390)
+++ runtime/vm/gc_marker.h	(working copy)
@@ -22,7 +22,7 @@
 // of the mark-sweep collection. The marking bit used is defined in RawObject.
 class GCMarker : public ValueObject {
  public:
-  explicit GCMarker(Heap* heap) : heap_(heap) { }
+  explicit GCMarker(Heap* heap) : heap_(heap), marked_bytes_(0) { }
   ~GCMarker() { }
 
   void MarkObjects(Isolate* isolate,
@@ -30,6 +30,8 @@
                    bool invoke_api_callbacks,
                    bool collect_code);
 
+  intptr_t marked_words() { return marked_bytes_ >> kWordSizeLog2; }
+
  private:
   void Prologue(Isolate* isolate, bool invoke_api_callbacks);
   void Epilogue(Isolate* isolate, bool invoke_api_callbacks);
@@ -47,6 +49,7 @@
 
 
   Heap* heap_;
+  intptr_t marked_bytes_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(GCMarker);
 };