Schedule garbage collection on worker threads using idle tasks

Source/core/workers/WorkerThread.h

Index: Source/core/workers/WorkerThread.h
diff --git a/Source/core/workers/WorkerThread.h b/Source/core/workers/WorkerThread.h
index e6d67fa01cdacbe3a8d26eee247a1bc54b487237..0e16eb908d0083bc6c3ff695126611973a94876a 100644
--- a/Source/core/workers/WorkerThread.h
+++ b/Source/core/workers/WorkerThread.h
@@ -128,8 +128,12 @@ protected:
     virtual void destroyIsolate();
     virtual void terminateV8Execution();
 
+    // This is protected virtual for testing.
+    virtual bool doIdleGc(double deadlineSeconds);
+
 private:
     friend class WorkerSharedTimer;
+    friend class WorkerThreadIdleTask;
     friend class WorkerMicrotaskRunner;
 
     void stopInShutdownSequence();
@@ -137,7 +141,7 @@ private:
 
     void initialize();
     void shutdown();
-    void idleHandler();
+    void performIdleWork(double deadlineSeconds);
     void postDelayedTask(PassOwnPtr<ExecutionContextTask>, long long delayMs);
     void postDelayedTask(const WebTraceLocation&, PassOwnPtr<ExecutionContextTask>, long long delayMs);
 
@@ -148,6 +152,7 @@ private:
 
     RefPtr<WorkerLoaderProxy> m_workerLoaderProxy;
     WorkerReportingProxy& m_workerReportingProxy;
+    RawPtr<WebScheduler> m_webScheduler; // Not owned.
 
     RefPtrWillBePersistent<WorkerInspectorController> m_workerInspectorController;
     Mutex m_workerInspectorControllerMutex;