Hide NSAutoreleasePool from ARC translation units.

base/message_loop/message_pump_mac.mm

Index: base/message_loop/message_pump_mac.mm
diff --git a/base/message_loop/message_pump_mac.mm b/base/message_loop/message_pump_mac.mm
index 9a8e95a6e190a3db2c422b9efe79f5e87e2e45da..891cc347448ff70b30f9357ff431d46aad613f59 100644
--- a/base/message_loop/message_pump_mac.mm
+++ b/base/message_loop/message_pump_mac.mm
@@ -697,7 +697,7 @@ void MessagePumpCFRunLoopBase::EnterExitRunLoop(CFRunLoopActivity activity) {
 }
 
 // Base version returns a standard NSAutoreleasePool.
-NSAutoreleasePool* MessagePumpCFRunLoopBase::CreateAutoreleasePool() {
+AutoreleasePoolType* MessagePumpCFRunLoopBase::CreateAutoreleasePool() {
   return [[NSAutoreleasePool alloc] init];
 }
 
@@ -909,7 +909,7 @@ MessagePumpCrApplication::~MessagePumpCrApplication() {
 // CrApplication is responsible for setting handlingSendEvent to true just
 // before it sends the event through the event handling mechanism, and
 // returning it to its previous value once the event has been sent.
-NSAutoreleasePool* MessagePumpCrApplication::CreateAutoreleasePool() {
+AutoreleasePoolType* MessagePumpCrApplication::CreateAutoreleasePool() {
   if (MessagePumpMac::IsHandlingSendEvent())
     return nil;
   return MessagePumpNSApplication::CreateAutoreleasePool();