Fix compile failure on Win64 introduced in r12291.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 2ec740c08c8ab1ae25e621993419599a34c2ee7f..8cc1dea87ea5567a12deb3443342758ea756ded9 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -462,13 +462,13 @@ void Heap::GarbageCollectionEpilogue() {
             (cell_space()->CommittedMemory() * 100.0) / CommittedMemory()));
 
     isolate_->counters()->heap_sample_total_committed()->AddSample(
-        CommittedMemory() / KB);
+        static_cast<int>(CommittedMemory() / KB));
     isolate_->counters()->heap_sample_total_used()->AddSample(
-        SizeOfObjects() / KB);
+        static_cast<int>(SizeOfObjects() / KB));
     isolate_->counters()->heap_sample_map_space_committed()->AddSample(
-        map_space()->CommittedMemory() / KB);
+        static_cast<int>(map_space()->CommittedMemory() / KB));
     isolate_->counters()->heap_sample_cell_space_committed()->AddSample(
-        cell_space()->CommittedMemory() / KB);
+        static_cast<int>(cell_space()->CommittedMemory() / KB));
   }
 
 #define UPDATE_COUNTERS_FOR_SPACE(space)                                       \