Add WorkerThread based methods for start/stop of worker threads.

content/child/blink_platform_impl.cc

Index: content/child/blink_platform_impl.cc
diff --git a/content/child/blink_platform_impl.cc b/content/child/blink_platform_impl.cc
index f0544a86736951fe7c57badf7392f37adb9a21d4..629b90edfb6b89934d3e7c83420014409c718a5c 100644
--- a/content/child/blink_platform_impl.cc
+++ b/content/child/blink_platform_impl.cc
@@ -922,6 +922,16 @@ void BlinkPlatformImpl::didStopWorkerRunLoop(
   worker_task_runner->OnWorkerRunLoopStopped(runLoop);
 }
 
+void BlinkPlatformImpl::didStartWorkerThread(blink::WebThread* thread) {
+  WorkerTaskRunner* worker_task_runner = WorkerTaskRunner::Instance();
+  worker_task_runner->OnWorkerThreadStarted(thread);
+}
+
+void BlinkPlatformImpl::didStopWorkerThread(blink::WebThread* thread) {
+  WorkerTaskRunner* worker_task_runner = WorkerTaskRunner::Instance();
+  worker_task_runner->OnWorkerThreadStopped(thread);
+}
+
 blink::WebCrypto* BlinkPlatformImpl::crypto() {
   WebCryptoImpl::EnsureInit();
   return &web_crypto_;