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

Source/core/inspector/InspectorTracingAgent.cpp

 //
 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 
 #include "config.h"
 
 #include "core/inspector/InspectorTracingAgent.h"
 
@@ skipping 22 matching lines @@
 {
 }
 
 void InspectorTracingAgent::restore()
 {
     emitMetadataEvents();
 }
 
 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();
     callback->sendSuccess();
 }
 
 void InspectorTracingAgent::end(ErrorString* errorString, PassRefPtrWillBeRawPtr<EndCallback> callback)
 {
     m_client->disableTracing();
-    m_workerAgent->setTracingSessionId(String());
+    resetSessionId();
     callback->sendSuccess();
 }
 
 String InspectorTracingAgent::sessionId()
 {
     return m_state->getString(TracingAgentState::sessionId);
 }
 
 void InspectorTracingAgent::emitMetadataEvents()
 {
     TRACE_EVENT_INSTANT1(devtoolsMetadataEventCategory, "TracingStartedInPage", "sessionId", sessionId().utf8());
     if (m_layerTreeId)
         setLayerTreeId(m_layerTreeId);
     m_workerAgent->setTracingSessionId(sessionId());
 }
 
 void InspectorTracingAgent::setLayerTreeId(int layerTreeId)
 {
     m_layerTreeId = layerTreeId;
     TRACE_EVENT_INSTANT2(devtoolsMetadataEventCategory, "SetLayerTreeId", "sessionId", sessionId().utf8(), "layerTreeId", m_layerTreeId);
 }
 
 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());
+}
+
+}