Only zapped used handles if a handle scope fits entirely within one handle block

This should avoid zapping the same unused handles over and over again
when using many small nested handle scopes.

BUG=none
R=mstarzinger@chromium.org, vegorov@chromium.org

Review URL: https://codereview.chromium.org/24359003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16987 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/handles-inl.h

@@ -130,16 +130,17 @@ void HandleScope::CloseScope(Isolate* isolate,
   v8::ImplementationUtilities::HandleScopeData* current =
       isolate->handle_scope_data();
 
-  current->next = prev_next;
+  std::swap(current->next, prev_next);
   current->level--;
   if (current->limit != prev_limit) {
     current->limit = prev_limit;
     DeleteExtensions(isolate);
-  }
-
 #ifdef ENABLE_EXTRA_CHECKS
-  ZapRange(prev_next, prev_limit);
+    ZapRange(current->next, prev_limit);
+  } else {
+    ZapRange(current->next, prev_next);
 #endif
+  }
 }