Make Win64 compile.

src/incremental-marking.cc

Index: src/incremental-marking.cc
diff --git a/src/incremental-marking.cc b/src/incremental-marking.cc
index 436aae0c364f8b60badb6753ee621b0da2c11173..5cc96ad5262de17b9d08e83f8d3251c2f038fbbd 100644
--- a/src/incremental-marking.cc
+++ b/src/incremental-marking.cc
@@ -397,7 +397,7 @@ void IncrementalMarking::StartMarking() {
 
   // Initialize marking stack.
   Address addr = static_cast<Address>(marking_deque_memory_->address());
-  int size = marking_deque_memory_->size();
+  size_t size = marking_deque_memory_->size();
   if (FLAG_force_marking_deque_overflows) size = 64 * kPointerSize;
   marking_deque_.Initialize(addr, addr + size);
 
@@ -462,7 +462,7 @@ void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
       ASSERT(Marking::IsGrey(Marking::MarkBitFrom(obj)));
     }
   }
-  marking_deque_.set_top(new_top);
+  marking_deque_.set_top(static_cast<int>(new_top));
 
   steps_took_since_last_gc_ = 0;
   steps_count_since_last_gc_ = 0;