DevTools: add Tracing agent on back-end

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
new file mode 100644
index 0000000000000000000000000000000000000000..cb81ec83148d739fba030d7ea391f61b52c28bb4
--- /dev/null
+++ b/Source/core/inspector/InspectorTracingAgent.cpp
@@ -0,0 +1,68 @@
+//
+// 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 "platform/TraceEvent.h"
+
+namespace WebCore {
+
+namespace TracingAgentState {
+const char sessionId[] = "sessionId";
+}
+
+namespace {
+const char devtoolsMetadataEventCategory[] = TRACE_DISABLED_BY_DEFAULT("devtools.timeline");
+}
+
+InspectorTracingAgent::InspectorTracingAgent()
+    : InspectorBaseAgent<InspectorTracingAgent>("Tracing")
+    , m_layerTreeId(0)
+{
+}
+
+void InspectorTracingAgent::restore()
+{
+    emitMetadataEvents();
+}
+
+void InspectorTracingAgent::start(ErrorString*, const String&, const String&, const double*, String* outSessionId)
+{
+    innerStart();
+    *outSessionId = sessionId();
+}
+
+void InspectorTracingAgent::innerStart()
+{
+    String sessionId = IdentifiersFactory::createIdentifier();
+    m_state->setString(TracingAgentState::sessionId, sessionId);
+    emitMetadataEvents();
+}
+
+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);
+}
+
+void InspectorTracingAgent::setLayerTreeId(int layerTreeId)
+{
+    m_layerTreeId = layerTreeId;
+    TRACE_EVENT_INSTANT2(devtoolsMetadataEventCategory, "SetLayerTreeId", "sessionId", sessionId().utf8(), "layerTreeId", m_layerTreeId);
+}
+
+}