arc: enable Android tracing from chrome://tracing in dev mode

chromeos/trace/arc_tracing_agent.h

+// Copyright 2017 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 CHROMEOS_TRACE_ARC_TRACING_AGENT_H_
+#define CHROMEOS_TRACE_ARC_TRACING_AGENT_H_
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/trace_event/trace_event.h"
+#include "base/trace_event/tracing_agent.h"
+#include "chromeos/chromeos_export.h"
+
+namespace chromeos {
+
+// A wrapper for controlling tracing in ARC container.
+// The overriden Stop/StartAgentTracing functions are implemented by the
+// Delegate object to interact with ARC bridge. All the functions are expected
+// to be called on the browser's UI thread.
+class CHROMEOS_EXPORT ArcTracingAgent : public base::trace_event::TracingAgent {
+ public:
+  class Delegate {
+   public:
+    // Callback for StartTracing, takes one boolean argument to indicate
+    // success or fail.

[Daniel Erat, 2017/03/08 15:41:14]

nit: s/fail/failure/

[Earl Ou, 2017/03/09 06:08:42]

Done.

+    using StartTracingCallback = base::Callback<void(bool)>;
+    // Callback for StopTracing, takes one boolean argument to indicate
+    // success or fail.

[Daniel Erat, 2017/03/08 15:41:14]

nit: s/fail/failure/

[Earl Ou, 2017/03/09 06:08:42]

Done.

+    using StopTracingCallback = base::Callback<void(bool)>;
+
+    virtual ~Delegate();
+
+    // Starts tracing in ARC container.
+    virtual void StartTracing(
+        const base::trace_event::TraceConfig& trace_config,
+        const StartTracingCallback& callback) = 0;
+
+    // Stops tracing in ARC container.
+    virtual void StopTracing(const StopTracingCallback& callback) = 0;
+  };
+
+  ArcTracingAgent();
+  ~ArcTracingAgent() override;
+
+  static ArcTracingAgent* GetInstance();
+
+  // Sets Delegate instance, which should implement the communication
+  // using ARC bridge. If set to nullptr, calling of Start/StopAgentTracing
+  // does nothing. Note that this class doesn't have the ownership of
+  // |delegate| as it should be managed by |ArcServiceLauncher|

[Daniel Erat, 2017/03/08 15:41:14]

nit: i'd just say "Ownership of |delegate| remains with the caller." so this
comment doesn't get out of date if/when the delegate is moved in the future.
(also, referring to this outside class here is a bit of a layering violation.)

[Earl Ou, 2017/03/09 06:08:42]

Done.

+  virtual void SetDelegate(Delegate* delegate) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ArcTracingAgent);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROMEOS_TRACE_ARC_TRACING_AGENT_H_