- Address review comments from https://codereview.chromium.org/474913004/

runtime/vm/thread_pool_test.cc

Index: runtime/vm/thread_pool_test.cc
===================================================================
--- runtime/vm/thread_pool_test.cc	(revision 39411)
+++ runtime/vm/thread_pool_test.cc	(working copy)
@@ -35,7 +35,7 @@
       : sync_(sync), done_(done) {
   }
 
-  void Run() {
+  virtual void Run() {
     MonitorLocker ml(sync_);
     *done_ = true;
     ml.Notify();
@@ -92,7 +92,7 @@
       : millis_(millis) {
   }
 
-  void Run() {
+  virtual void Run() {
     OS::Sleep(millis_);
   }
 
@@ -166,7 +166,7 @@
       : pool_(pool), sync_(sync), todo_(todo), total_(total), done_(done) {
   }
 
-  void Run() {
+  virtual void Run() {
     todo_--;  // Subtract one for current task.
     int child_todo = todo_ / 2;