DevTools: tracing: remove state management from InspectorTracingAgent.

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 bdeffaeb254215199a670f243bf0c7f813258ea9..8e8edac01e7a874a5244db6f0744005010bf7627 100644
--- a/Source/core/inspector/InspectorTracingAgent.cpp
+++ b/Source/core/inspector/InspectorTracingAgent.cpp
@@ -18,7 +18,6 @@ namespace blink {
 
 namespace TracingAgentState {
 const char sessionId[] = "sessionId";
-const char tracingStarted[] = "tracingStarted";
 }
 
 namespace {
@@ -41,12 +40,7 @@ void InspectorTracingAgent::restore()
 
 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();
@@ -55,7 +49,6 @@ void InspectorTracingAgent::start(ErrorString*, const String& categoryFilter, co
 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();
 }
@@ -67,8 +60,6 @@ String InspectorTracingAgent::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);