DevTools: tracing: remove state management from InspectorTracingAgent.

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"
 
 #include "core/inspector/IdentifiersFactory.h"
 #include "core/inspector/InspectorClient.h"
 #include "core/inspector/InspectorState.h"
 #include "core/inspector/InspectorWorkerAgent.h"
 #include "platform/TraceEvent.h"
 
 namespace blink {
 
 namespace TracingAgentState {
 const char sessionId[] = "sessionId";
-const char tracingStarted[] = "tracingStarted";
 }
 
 namespace {
 const char devtoolsMetadataEventCategory[] = TRACE_DISABLED_BY_DEFAULT("devtools.timeline");
 }
 
 InspectorTracingAgent::InspectorTracingAgent(InspectorClient* client, InspectorWorkerAgent* workerAgent)
     : InspectorBaseAgent<InspectorTracingAgent>("Tracing")
     , m_layerTreeId(0)
     , m_client(client)
     , m_frontend(0)
     , m_workerAgent(workerAgent)
 {
 }
 
 void InspectorTracingAgent::restore()
 {
     emitMetadataEvents();
 }
 
 void InspectorTracingAgent::start(ErrorString*, const String& categoryFilter, const String&, const double*, PassRefPtrWillBeRawPtr<StartCallback> callback)
 {
-    if (m_state->getBoolean(TracingAgentState::tracingStarted)) {

[yurys, 2014/10/15 08:43:46]

I believe we'd better return an error when tracing is already started. It can be
determined at this point by checking whether
m_state->getString(TracingAgentState::sessionId) is empty.

[yurys, 2014/10/15 08:46:23]

It can be a DCHECK since we reject such requests on the browser side:
https://code.google.com/p/chromium/codesearch#chromium/src/content/browser/de...

-        callback->sendSuccess();
-        return;
-    }
     m_state->setString(TracingAgentState::sessionId, IdentifiersFactory::createIdentifier());
-    m_state->setBoolean(TracingAgentState::tracingStarted, true);
     m_client->enableTracing(categoryFilter);
     emitMetadataEvents();
     callback->sendSuccess();
 }
 
 void InspectorTracingAgent::end(ErrorString* errorString, PassRefPtrWillBeRawPtr<EndCallback> callback)
 {
     m_client->disableTracing();
-    m_state->setBoolean(TracingAgentState::tracingStarted, false);

[yurys, 2014/10/15 08:43:46]

This is not enough as after front-end disconnect we will still have non-empty
sessionId in the state. We should clear it on front-end disconnect.

     m_workerAgent->setTracingSessionId(String());
     callback->sendSuccess();
 }
 
 String InspectorTracingAgent::sessionId()
 {
     return m_state->getString(TracingAgentState::sessionId);
 }
 
 void InspectorTracingAgent::emitMetadataEvents()
 {
-    if (!m_state->getBoolean(TracingAgentState::tracingStarted))
-        return;
     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();
 }
 
 }