Use the new MX_PROCESS_SIGNALED signal name

runtime/bin/process_fuchsia.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #if !defined(DART_IO_DISABLED)
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_FUCHSIA)
 
 #include "bin/process.h"
@@ skipping 370 matching lines @@
     const intptr_t last = item_count_ - 1;
     items_[idx].handle = MX_HANDLE_INVALID;
     items_[idx].waitfor = MX_SIGNAL_NONE;
     items_[idx].pending = MX_SIGNAL_NONE;
     if (idx != last) {
       items_[idx] = items_[last];
     }
     item_count_--;
   }
 
-  // Interrupt message pipe.
+  // Interrupt channel.
   static mx_handle_t interrupt_in_;
   static mx_handle_t interrupt_out_;
 
   // Accessed only by the ExitCodeHandler thread.
   static mx_wait_item_t* items_;
   static intptr_t* items_to_remove_;
   static intptr_t item_count_;
   static intptr_t item_capacity_;
 
   // Protected by monitor_.
@@ skipping 413 matching lines @@
 void Process::ClearSignalHandler(intptr_t signal) {
   UNIMPLEMENTED();
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)
 
 #endif  // !defined(DART_IO_DISABLED)