Use gender neutral terms in heap.cc

BUG=
LOG=no

Review-Url: https://codereview.chromium.org/2084823004
Cr-Commit-Position: refs/heads/master@{#37190}

src/heap/heap.cc

@@ -1628,7 +1628,7 @@ void Heap::Scavenge() {
   scavenge_collector_->SelectScavengingVisitorsTable();
 
   if (UsingEmbedderHeapTracer()) {
-    // Register found wrappers with embedder so he can add them to his marking
+    // Register found wrappers with embedder so it can add them to its marking
     // deque and correctly manage the case when v8 scavenger collects the
     // wrappers by either keeping wrappables alive, or cleaning marking deque.
     mark_compact_collector()->RegisterWrappersWithEmbedderHeapTracer();