Remove DeviceMonitorLinux::WillDestroyCurrentMessageLoop().

device/base/device_monitor_linux.cc

Index: device/base/device_monitor_linux.cc
diff --git a/device/base/device_monitor_linux.cc b/device/base/device_monitor_linux.cc
index 179b6f5bae295812a64370145dd0c79445e049ef..67ce6b8af3a8de841344944d9ef5dffa62ed9134 100644
--- a/device/base/device_monitor_linux.cc
+++ b/device/base/device_monitor_linux.cc
@@ -29,7 +29,6 @@ base::LazyInstance<DeviceMonitorLinux>::Leaky g_device_monitor_linux =
 
 DeviceMonitorLinux::DeviceMonitorLinux() : monitor_fd_(-1) {
   base::ThreadRestrictions::AssertIOAllowed();
-  base::MessageLoop::current()->AddDestructionObserver(this);
 
   udev_.reset(udev_new());
   if (!udev_) {
@@ -100,12 +99,6 @@ void DeviceMonitorLinux::Enumerate(const EnumerateCallback& callback) {
   }
 }
 
-void DeviceMonitorLinux::WillDestroyCurrentMessageLoop() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  for (auto& observer : observers_)
-    observer.WillDestroyMonitorMessageLoop();
-}
-
 DeviceMonitorLinux::~DeviceMonitorLinux() {
   // A leaky LazyInstance is never destroyed.
   NOTREACHED();