Worker: Introduce an observation mechanism for WorkerThread termination

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

Index: third_party/WebKit/Source/core/workers/WorkerThread.cpp
diff --git a/third_party/WebKit/Source/core/workers/WorkerThread.cpp b/third_party/WebKit/Source/core/workers/WorkerThread.cpp
index 62c4fd888ac86f03869271c109be5607ccb159c8..2697ed03c31de02f4fafe799903ce86dafea5748 100644
--- a/third_party/WebKit/Source/core/workers/WorkerThread.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerThread.cpp
@@ -37,7 +37,9 @@
 #include "core/workers/WorkerBackingThread.h"
 #include "core/workers/WorkerClients.h"
 #include "core/workers/WorkerReportingProxy.h"
+#include "core/workers/WorkerThreadLifecycleObserver.h"
 #include "core/workers/WorkerThreadStartupData.h"
+#include "platform/LifecycleNotifier.h"
 #include "platform/ThreadSafeFunctional.h"
 #include "platform/WaitableEvent.h"
 #include "platform/WebThreadSupportingGC.h"
@@ -292,6 +294,7 @@ WorkerThread::WorkerThread(PassRefPtr<WorkerLoaderProxy> workerLoaderProxy, Work
     , m_shutdownEvent(adoptPtr(new WaitableEvent(
         WaitableEvent::ResetPolicy::Manual,
         WaitableEvent::InitialState::NonSignaled)))
+    , m_workerThreadContext(new WorkerThreadContext)
 {
     MutexLocker lock(threadSetMutex());
     workerThreads().add(this);
@@ -339,6 +342,10 @@ void WorkerThread::terminateInternal(TerminationMode mode)
     if (m_terminationEvent)
         m_terminationEvent->signal();
 
+    DCHECK(m_workerThreadContext);
+    m_workerThreadContext->notifyContextDestroyed();
+    m_workerThreadContext = nullptr;
+
     // If the worker thread was never initialized, don't start another
     // shutdown, but still wait for the thread to signal when shutdown has
     // completed on initializeOnWorkerThread().