Allow PowerMonitorDeviceSource to be used from sequenced tasks.

base/power_monitor/power_monitor_device_source.cc

Index: base/power_monitor/power_monitor_device_source.cc
diff --git a/base/power_monitor/power_monitor_device_source.cc b/base/power_monitor/power_monitor_device_source.cc
index d7060c2a228c12f4b3f4acb70b86c486aa526db1..5df58003375c60009362165b0745c15bae937a5c 100644
--- a/base/power_monitor/power_monitor_device_source.cc
+++ b/base/power_monitor/power_monitor_device_source.cc
@@ -4,13 +4,9 @@
 
 #include "base/power_monitor/power_monitor_device_source.h"
 
-#include "base/threading/thread_task_runner_handle.h"
-
 namespace base {
 
 PowerMonitorDeviceSource::PowerMonitorDeviceSource() {
-  DCHECK(ThreadTaskRunnerHandle::IsSet());
-
 #if defined(OS_MACOSX)
   PlatformInit();
 #endif