Build targets from mojo_base on iOS

mojo/system/message_pipe_test_utils.cc

Index: mojo/system/message_pipe_test_utils.cc
diff --git a/mojo/system/message_pipe_test_utils.cc b/mojo/system/message_pipe_test_utils.cc
index 37284ce24849253a8dfb5581507d97bd94b4aac3..786c23ae1874b10b6b074c998d11d678c541f557 100644
--- a/mojo/system/message_pipe_test_utils.cc
+++ b/mojo/system/message_pipe_test_utils.cc
@@ -94,6 +94,7 @@ void ChannelThread::ShutdownChannelOnIOThread() {
   channel_ = NULL;
 }
 
+#if !defined(OS_IOS)
 MultiprocessMessagePipeTestBase::MultiprocessMessagePipeTestBase()
     : channel_thread_(&platform_support_) {
 }
@@ -104,6 +105,7 @@ MultiprocessMessagePipeTestBase::~MultiprocessMessagePipeTestBase() {
 void MultiprocessMessagePipeTestBase::Init(scoped_refptr<MessagePipe> mp) {
   channel_thread_.Start(helper_.server_platform_handle.Pass(), mp);
 }
+#endif
 
 }  // namespace test
 }  // namespace system