[TimeZoneMonitor] Decouple renderer side impl from content to blink.

third_party/WebKit/Source/core/workers/WorkerThread.h

Index: third_party/WebKit/Source/core/workers/WorkerThread.h
diff --git a/third_party/WebKit/Source/core/workers/WorkerThread.h b/third_party/WebKit/Source/core/workers/WorkerThread.h
index bbd47ae68ee551bb842c78c0e912805c0fd74706..2725d6c335a1ae0de43ccd8a09c52d22cf18dd1c 100644
--- a/third_party/WebKit/Source/core/workers/WorkerThread.h
+++ b/third_party/WebKit/Source/core/workers/WorkerThread.h
@@ -159,6 +159,10 @@ class CORE_EXPORT WorkerThread : public WebThread::TaskObserver {
   // Number of active worker threads.
   static unsigned workerThreadCount();
 
+  // Returns a set of all worker threads. This must be called only on the main
+  // thread and the returned set must not be stored for future use.
+  static HashSet<WorkerThread*>& workerThreads();
+
   PlatformThreadId platformThreadId();
 
   bool isForciblyTerminated();