Made iteration of global handles more efficient on scavenges.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index 5a3ab890572763004f7570d0d8e6440c2676949c..785462e506a73cdcbb93f84e81cafe1e44a82b9e 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -593,7 +593,7 @@ void MarkCompactCollector::MarkSymbolTable() {
 void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
   // Mark the heap roots including global variables, stack variables,
   // etc., and all objects reachable from them.
-  Heap::IterateStrongRoots(visitor);
+  Heap::IterateStrongRoots(visitor, VISIT_ONLY_STRONG);
 
   // Handle the symbol table specially.
   MarkSymbolTable();
@@ -1455,7 +1455,7 @@ void MarkCompactCollector::UpdatePointers() {
   state_ = UPDATE_POINTERS;
 #endif
   UpdatingVisitor updating_visitor;
-  Heap::IterateRoots(&updating_visitor);
+  Heap::IterateRoots(&updating_visitor, VISIT_ONLY_STRONG);
   GlobalHandles::IterateWeakRoots(&updating_visitor);
 
   int live_maps = IterateLiveObjects(Heap::map_space(),