Adds a callback to TracingAgent::StartAgentTracing()

base/trace_event/tracing_agent.h

 // Copyright 2015 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 BASE_TRACE_EVENT_TRACING_AGENT_H_
 #define BASE_TRACE_EVENT_TRACING_AGENT_H_
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/values.h"
 
 namespace base {
 
 class TimeTicks;
 
 namespace trace_event {
 
 class TraceConfig;
 
 // A tracing agent is an entity that records its own sort of trace. Each
 // tracing method that produces its own trace log should implement this
 // interface. All tracing agents must only be controlled by TracingController.
 // Some existing examples include TracingControllerImpl for Chrome trace events,
 // DebugDaemonClient for CrOs system trace, EtwSystemEventConsumer for Windows
 // system trace and PowerTracingAgent for BattOr power trace.
 class BASE_EXPORT TracingAgent {
  public:
+  using StartAgentTracingCallback =
+      base::Callback<void(const std::string& agent_name, bool success)>;
   using StopAgentTracingCallback = base::Callback<void(
       const std::string& agent_name,
       const std::string& events_label,
       const scoped_refptr<base::RefCountedString>& events_str_ptr)>;
   using RecordClockSyncMarkerCallback = base::Callback<void(
       int sync_id,
       const TimeTicks& issue_ts,
       const TimeTicks& issue_end_ts)>;
 
   virtual ~TracingAgent();
 
   // Gets the name of the tracing agent. Each tracing agent's name should be
   // unique.
   virtual std::string GetTracingAgentName() = 0;
 
   // Gets the trace event label of this tracing agent. The label will be used to
   // label this agent's trace when all traces from different tracing agents are
   // combined. Multiple tracing agents could have the same label. The tracing
   // agents using the same label should not be able to run at the same time. For
   // example, ETW on Windows and CrOS system tracing both use
   // "systemTraceEvents" as the label. Those two agents never run at the same
   // time because they are for different platforms.
   virtual std::string GetTraceEventLabel() = 0;
 
   // Starts tracing on the tracing agent with the trace configuration.
-  virtual bool StartAgentTracing(const TraceConfig& trace_config) = 0;
+  virtual void StartAgentTracing(const TraceConfig& trace_config,
+                                 const StartAgentTracingCallback& callback) = 0;
 
   // Stops tracing on the tracing agent. The trace data will be passed back to
   // the TracingController via the callback.
   virtual void StopAgentTracing(const StopAgentTracingCallback& callback) = 0;
 
   // Checks if the tracing agent supports explicit clock synchronization.
   virtual bool SupportsExplicitClockSync();
 
   // Records a clock sync marker issued by another tracing agent. This is only
   // used if the tracing agent supports explicit clock synchronization.
@@ skipping 18 matching lines @@
   // is true in Chrome because all agent threads' clocks are Chrome clock.
   virtual void RecordClockSyncMarker(
       int sync_id,
       const RecordClockSyncMarkerCallback& callback);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACING_AGENT_H_