Revert of Remove WorkerBackingThread::scriptCount

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

Index: third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
diff --git a/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp b/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
index 0c7ae4efb3310091956e20fad3e1a35a59b29ed2..5f047754968455dde26cdd81309861c94377b751 100644
--- a/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
+++ b/third_party/WebKit/Source/core/workers/WorkerBackingThread.cpp
@@ -61,6 +61,30 @@
 
 WorkerBackingThread::~WorkerBackingThread()
 {
+#if DCHECK_IS_ON()
+    MutexLocker locker(m_mutex);
+    DCHECK_EQ(0u, m_workerScriptCount);
+#endif
+}
+
+void WorkerBackingThread::attach()
+{
+    {
+        MutexLocker locker(m_mutex);
+        if (++m_workerScriptCount > 1)
+            return;
+    }
+    initialize();
+}
+
+void WorkerBackingThread::detach()
+{
+    {
+        MutexLocker locker(m_mutex);
+        if (--m_workerScriptCount > 0)
+            return;
+    }
+    shutdown();
 }
 
 void WorkerBackingThread::initialize()