Record DevTools metadata events on worker threads when starting recoring tracing based Timeline

Source/core/workers/WorkerMessagingProxy.cpp

Index: Source/core/workers/WorkerMessagingProxy.cpp
diff --git a/Source/core/workers/WorkerMessagingProxy.cpp b/Source/core/workers/WorkerMessagingProxy.cpp
index 081a68272cb06abb18d032731482785d41c54941..46d09cffd0fab2db4b6f4f50a8110a102e3255d4 100644
--- a/Source/core/workers/WorkerMessagingProxy.cpp
+++ b/Source/core/workers/WorkerMessagingProxy.cpp
@@ -48,6 +48,7 @@
 #include "core/workers/WorkerObjectProxy.h"
 #include "core/workers/WorkerThreadStartupData.h"
 #include "platform/NotImplemented.h"
+#include "platform/TraceEvent.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Functional.h"
 #include "wtf/MainThread.h"
@@ -253,6 +254,22 @@ void WorkerMessagingProxy::sendMessageToInspector(const String& message)
     m_workerThread->interruptAndDispatchInspectorCommands();
 }
 
+static void dispatchWriteTimelineStartedEvent(ExecutionContext* context, const String& sessionId)
+{
+    TRACE_EVENT_INSTANT1(TRACE_DISABLED_BY_DEFAULT("devtools.timeline"), "TracingStartedInWorker", "sessionId", sessionId.utf8());
+}
+
+void WorkerMessagingProxy::writeTimelineStartedEvent(const String& sessionId)
+{
+    if (m_askedToTerminate)
+        return;
+    OwnPtr<ExecutionContextTask> task = createCrossThreadTask(dispatchWriteTimelineStartedEvent, String(sessionId));
+    if (m_workerThread)
+        m_workerThread->postTask(task.release());
+    else
+        m_queuedEarlyTasks.append(task.release());
+}
+
 void WorkerMessagingProxy::workerGlobalScopeDestroyed()
 {
     // This method is always the last to be performed, so the proxy is not needed for communication