Fix invalid use of int in Zone.

src/lithium-allocator.cc

Index: src/lithium-allocator.cc
diff --git a/src/lithium-allocator.cc b/src/lithium-allocator.cc
index 3b9285689751aba6ea4ab9c4ae6f60605b3a11fb..36c8c7d90a07ef9f6eb7f2e5dbe9c81575ae21b9 100644
--- a/src/lithium-allocator.cc
+++ b/src/lithium-allocator.cc
@@ -2174,8 +2174,8 @@ LAllocatorPhase::LAllocatorPhase(const char* name, LAllocator* allocator)
 
 LAllocatorPhase::~LAllocatorPhase() {
   if (FLAG_hydrogen_stats) {
-    unsigned size = allocator_->zone()->allocation_size() -
-                    allocator_zone_start_allocation_size_;
+    size_t size = allocator_->zone()->allocation_size() -
+                  allocator_zone_start_allocation_size_;
     isolate()->GetHStatistics()->SaveTiming(name(), base::TimeDelta(), size);
   }