DevTools: clear session id. follow-up patch after r183608

Source/core/inspector/InspectorTracingAgent.cpp

Index: Source/core/inspector/InspectorTracingAgent.cpp
diff --git a/Source/core/inspector/InspectorTracingAgent.cpp b/Source/core/inspector/InspectorTracingAgent.cpp
index 8e8edac01e7a874a5244db6f0744005010bf7627..6930a940d76c5664eabc0e7cd0d0133b56aa0f7a 100644
--- a/Source/core/inspector/InspectorTracingAgent.cpp
+++ b/Source/core/inspector/InspectorTracingAgent.cpp
@@ -40,6 +40,7 @@ void InspectorTracingAgent::restore()
 
 void InspectorTracingAgent::start(ErrorString*, const String& categoryFilter, const String&, const double*, PassRefPtrWillBeRawPtr<StartCallback> callback)
 {
+    ASSERT(m_state->getString(TracingAgentState::sessionId).isEmpty());
     m_state->setString(TracingAgentState::sessionId, IdentifiersFactory::createIdentifier());
     m_client->enableTracing(categoryFilter);
     emitMetadataEvents();
@@ -49,7 +50,7 @@ void InspectorTracingAgent::start(ErrorString*, const String& categoryFilter, co
 void InspectorTracingAgent::end(ErrorString* errorString, PassRefPtrWillBeRawPtr<EndCallback> callback)
 {
     m_client->disableTracing();
-    m_workerAgent->setTracingSessionId(String());
+    resetSessionId();
     callback->sendSuccess();
 }
 
@@ -77,4 +78,15 @@ void InspectorTracingAgent::setFrontend(InspectorFrontend* frontend)
     m_frontend = frontend->tracing();
 }
 
+void InspectorTracingAgent::clearFrontend()
+{
+    resetSessionId();
+}
+
+void InspectorTracingAgent::resetSessionId()
+{
+    m_state->remove(TracingAgentState::sessionId);
+    m_workerAgent->setTracingSessionId(sessionId());
+}
+
 }