Remove did(Start|Stop)WorkerThread as it is not used.

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index 8e7a65e43d4f07b5d69d0d7366a0ce86354aa687..cc6dd47d36d85587033ce60e656a62b394b0d0cf 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -246,7 +246,7 @@ void WorkerThread::initialize()
         }
     }
 
-    // The corresponding call to didStopWorkerThread is in
+    // The corresponding call to didStopWorkerRunLoop is in
     // ~WorkerScriptController.
     blink::Platform::current()->didStartWorkerRunLoop(blink::WebWorkerRunLoop(this));