Enable the FileDescriptorWatcher API on MessageLoopForIO threads.

base/threading/thread.cc

Index: base/threading/thread.cc
diff --git a/base/threading/thread.cc b/base/threading/thread.cc
index 761bc871885ede525866ca4a6c3e6226cb0e3005..88025e96aa93ad6c2d39beaedcdad604bdced698 100644
--- a/base/threading/thread.cc
+++ b/base/threading/thread.cc
@@ -17,6 +17,10 @@
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 
+#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
+#include "base/files/file_descriptor_watcher_posix.h"
+#endif
+
 #if defined(OS_WIN)
 #include "base/win/scoped_com_initializer.h"
 #endif
@@ -295,6 +299,15 @@ void Thread::ThreadMain() {
   message_loop_->BindToCurrentThread();
   message_loop_->SetTimerSlack(message_loop_timer_slack_);
 
+#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
+  // Allow threads running a MessageLoopForIO to use FileDescriptorWatcher API.
+  std::unique_ptr<FileDescriptorWatcher> file_descriptor_watcher;
+  if (MessageLoopForIO::IsCurrent()) {
+    file_descriptor_watcher.reset(
+        new FileDescriptorWatcher(MessageLoopForIO::current()));

[dcheng, 2016/09/26 17:34:40]

Is there a time when this wouldn't return the same value as |message_loop_|?

[fdoray, 2016/09/26 17:44:07]

No.

message_loop_->BindToCurrentThread() above sets the TLS returned by
MessageLoopForIO::current(). Added DCHECK.

+  }
+#endif
+
 #if defined(OS_WIN)
   std::unique_ptr<win::ScopedCOMInitializer> com_initializer;
   if (com_status_ != NONE) {