Fix building with GCC 3.x

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 85a64ec77c082ce2cc5ddfda636ae1f1d808f71d..99b97f303130a4037a7e4d3079953dabdbfc5efc 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1154,7 +1154,7 @@ class Heap {
   Object* global_contexts_list() { return global_contexts_list_; }
 
   // Number of mark-sweeps.
-  int ms_count() { return ms_count_; }
+  unsigned int ms_count() { return ms_count_; }
 
   // Iterates over all roots in the heap.
   void IterateRoots(ObjectVisitor* v, VisitMode mode);
@@ -1698,7 +1698,7 @@ class Heap {
   // Returns the amount of external memory registered since last global gc.
   intptr_t PromotedExternalMemorySize();
 
-  int ms_count_;  // how many mark-sweep collections happened
+  unsigned int ms_count_;  // how many mark-sweep collections happened
   unsigned int gc_count_;  // how many gc happened
 
   // For post mortem debugging.