Use FileDescriptorWatcher in AlarmTimer.
This CL is identical to https://codereview.chromium.org/2398753003/
which was reverted % fixes to avoid memory leaks in tests.
FileDescriptorWatcher is a new API that replaces
MessageLoopForIO::WatchFileDescriptor.
This CL also gets rid of the base::Thread created in the anonymous
namespace of alarm_timer_chromeos.cc. The FileDescriptorWatcher
API is supported by every TaskScheduler thread. Very soon, most
tasks in Chrome will run in TaskScheduler. Therefore, there is no
reason to create a base::Thread to allow AlarmTimer to be used from
threads that don't support the FileDescriptorWatcher API.
BUG=645114
Review-Url: https://codereview.chromium.org/2405503002
Cr-Commit-Position: refs/heads/master@{#424471}
3 files changed
