Adds a callback to TracingAgent::StartAgentTracing()

chromeos/dbus/fake_debug_daemon_client.h

Index: chromeos/dbus/fake_debug_daemon_client.h
diff --git a/chromeos/dbus/fake_debug_daemon_client.h b/chromeos/dbus/fake_debug_daemon_client.h
index a75edbf33c43118c7d7762993cd2dedadabe3794..b7f7799ba650c778436da121bbd81228fcb8ec67 100644
--- a/chromeos/dbus/fake_debug_daemon_client.h
+++ b/chromeos/dbus/fake_debug_daemon_client.h
@@ -31,8 +31,8 @@ class CHROMEOS_EXPORT FakeDebugDaemonClient : public DebugDaemonClient {
                     const SetDebugModeCallback& callback) override;
   std::string GetTracingAgentName() override;
   std::string GetTraceEventLabel() override;
-  bool StartAgentTracing(
-      const base::trace_event::TraceConfig& trace_config) override;
+  void StartAgentTracing(const base::trace_event::TraceConfig& trace_config,
+                         const StartAgentTracingCallback& callback) override;
   void StopAgentTracing(const StopAgentTracingCallback& callback) override;
   void SetStopAgentTracingTaskRunner(
       scoped_refptr<base::TaskRunner> task_runner) override;