[BattOr] Make BattOr able to return firmware version.

content/browser/tracing/power_tracing_agent.cc

 // 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.
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
 #include "base/memory/singleton.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/trace_event/trace_event_impl.h"
 #include "content/browser/tracing/power_tracing_agent.h"
@@ skipping 163 matching lines @@
 
   record_clock_sync_marker_callback_.Reset();
   record_clock_sync_marker_sync_id_ = std::string();
   record_clock_sync_marker_start_time_ = base::TimeTicks();
 }
 
 bool PowerTracingAgent::SupportsExplicitClockSync() {
   return battor_agent_->SupportsExplicitClockSync();
 }
 
+void PowerTracingAgent::OnGetFirmwareGitHashComplete(
+    const std::string& version, battor::BattOrError error) {
+  return;
+}
+
 }  // namespace content