arc: enable Android tracing in verified-boot mode

chromeos/dbus/fake_arc_trace_agent.cc

+// Copyright 2016 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 "chromeos/dbus/fake_arc_trace_agent.h"
+
+#include <string>
+
+#include "base/single_thread_task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace chromeos {
+
+namespace {
+
+constexpr char kArcTracingAgentName[] = "arc";
+constexpr char kArcTraceLabel[] = "ArcTraceEvents";
+
+}  // namespace
+
+void FakeArcTraceAgent::SetDelegate(Delegate* delegate) {}
+
+void FakeArcTraceAgent::SetStopAgentTracingTaskRunner(
+    scoped_refptr<base::TaskRunner> task_runner) {}
+
+std::string FakeArcTraceAgent::GetTracingAgentName() {
+  return kArcTracingAgentName;
+}
+
+std::string FakeArcTraceAgent::GetTraceEventLabel() {
+  return kArcTraceLabel;
+}
+
+void FakeArcTraceAgent::StartAgentTracing(
+    const base::trace_event::TraceConfig& trace_config,
+    const StartAgentTracingCallback& callback) {
+  base::ThreadTaskRunnerHandle::Get()->PostTask(

[Luis Héctor Chávez, 2016/12/28 17:21:58]

callback.Run(GetTracingAgentName(), true /* success */);

(or comment why you need to use PostTask).

[shunhsingou, 2016/12/29 09:40:29]

Added a comment here.

I think this is something need to be modified in the tracing_controller_impl.cc.
It expects callback to be called after StartAgentTracing() and its caller
function returns.

+      FROM_HERE,
+      base::Bind(callback, GetTracingAgentName(), true /* success */));
+}
+
+void FakeArcTraceAgent::StopAgentTracing(
+    const StopAgentTracingCallback& callback) {
+  std::string no_data;
+  callback.Run(GetTracingAgentName(), GetTraceEventLabel(),
+               base::RefCountedString::TakeString(&no_data));
+}
+
+void FakeArcTraceAgent::Init(dbus::Bus* bus) {}
+
+}  // namespace chromeos