Update ChannelReader to use AttachmentBroker.

ipc/ipc_message.cc

Index: ipc/ipc_message.cc
diff --git a/ipc/ipc_message.cc b/ipc/ipc_message.cc
index fcdbb6aa6d5725fc17803a9d026e222dbac1ef7b..c8f7e84fc737cd20c384bcd8c8447c5773c5bd7c 100644
--- a/ipc/ipc_message.cc
+++ b/ipc/ipc_message.cc
@@ -73,9 +73,7 @@ Message::Message(const char* data, int data_len)
 
 Message::Message(const Message& other) : base::Pickle(other) {
   Init();
-#if defined(OS_POSIX)
   attachment_set_ = other.attachment_set_;
-#endif
 }
 
 void Message::Init() {
@@ -89,9 +87,7 @@ void Message::Init() {
 
 Message& Message::operator=(const Message& other) {
   *static_cast<base::Pickle*>(this) = other;
-#if defined(OS_POSIX)
   attachment_set_ = other.attachment_set_;
-#endif
   return *this;
 }