Provide an iOS message pump for IO implementation.

base/message_pump_libevent.cc

Index: base/message_pump_libevent.cc
diff --git a/base/message_pump_libevent.cc b/base/message_pump_libevent.cc
index 45e1bdb933aaeb8f92204939833c71c90f6f053a..b691eabd8d87320340c973931778d8078a8cd53e 100644
--- a/base/message_pump_libevent.cc
+++ b/base/message_pump_libevent.cc
@@ -144,22 +144,23 @@ MessagePumpLibevent::~MessagePumpLibevent() {
 
 bool MessagePumpLibevent::WatchFileDescriptor(int fd,
                                               bool persistent,
-                                              Mode mode,
+                                              int mode,
                                               FileDescriptorWatcher *controller,
                                               Watcher *delegate) {
   DCHECK_GE(fd, 0);
   DCHECK(controller);
   DCHECK(delegate);
-  DCHECK(mode == WATCH_READ || mode == WATCH_WRITE || mode == WATCH_READ_WRITE);
+  DCHECK(mode == WATCH_READ || mode == WATCH_WRITE ||
+         mode == (WATCH_READ | WATCH_WRITE));
   // WatchFileDescriptor should be called on the pump thread. It is not
   // threadsafe, and your watcher may never be registered.
   DCHECK(watch_file_descriptor_caller_checker_.CalledOnValidThread());
 
   int event_mask = persistent ? EV_PERSIST : 0;
-  if ((mode & WATCH_READ) != 0) {
+  if (mode & WATCH_READ) {
     event_mask |= EV_READ;
   }
-  if ((mode & WATCH_WRITE) != 0) {
+  if (mode & WATCH_WRITE) {
     event_mask |= EV_WRITE;
   }
 
@@ -190,12 +191,12 @@ bool MessagePumpLibevent::WatchFileDescriptor(int fd,
   event_set(evt.get(), fd, event_mask, OnLibeventNotification, controller);
 
   // Tell libevent which message pump this socket will belong to when we add it.
-  if (event_base_set(event_base_, evt.get()) != 0) {
+  if (event_base_set(event_base_, evt.get())) {
     return false;
   }
 
   // Add this socket to the list of monitored sockets.
-  if (event_add(evt.get(), NULL) != 0) {
+  if (event_add(evt.get(), NULL)) {
     return false;
   }