Refactor Pickle Read methods to use higher performance PickleIterator.

ipc/ipc_channel_posix.cc

Index: ipc/ipc_channel_posix.cc
diff --git a/ipc/ipc_channel_posix.cc b/ipc/ipc_channel_posix.cc
index 069869f3a8d9e722f1fdfb8c59979a36c13ec754..d772c28401bf944f7bd94f06ced8cd72fde29e3b 100644
--- a/ipc/ipc_channel_posix.cc
+++ b/ipc/ipc_channel_posix.cc
@@ -708,7 +708,7 @@ bool Channel::ChannelImpl::ProcessIncomingMessages() {
                  << " with type " << m.type() << " on fd " << pipe_;
         if (IsHelloMessage(&m)) {
           // The Hello message contains only the process id.
-          void *iter = NULL;
+          PickleReader iter(m);
           int pid;
           if (!m.ReadInt(&iter, &pid)) {
             NOTREACHED();