DevTools: add Tracing agent on back-end

Source/core/inspector/InspectorTracingAgent.h

+/*
+ * 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.
+ */
+
+#ifndef InspectorTracingAgent_h
+#define InspectorTracingAgent_h
+
+#include "InspectorFrontend.h"
+#include "core/inspector/InspectorBaseAgent.h"
+#include "wtf/PassOwnPtr.h"
+#include "wtf/text/WTFString.h"
+
+namespace WebCore {
+
+class InspectorClient;
+
+class InspectorTracingAgent FINAL
+    : public InspectorBaseAgent<InspectorTracingAgent>
+    , public InspectorBackendDispatcher::TracingCommandHandler {
+    WTF_MAKE_NONCOPYABLE(InspectorTracingAgent);
+public:
+    static PassOwnPtr<InspectorTracingAgent> create()
+    {
+        return adoptPtr(new InspectorTracingAgent());
+    }
+
+    // Base agent methods.
+    virtual void restore() OVERRIDE;
+
+    // Protocol method implementations.
+    virtual void start(ErrorString*, const String&, const String&, const double*, String* sessionId) OVERRIDE;
+
+    // Methods for other agents to use.
+    void setLayerTreeId(int);
+
+private:
+    InspectorTracingAgent();
+
+    void innerStart();
+    void emitMetadataEvents();
+    String sessionId();
+
+    int m_layerTreeId;
+};
+
+}
+
+#endif // InspectorTracingAgent_h