Don't use IsolateData for the exit hook as multiple embedders share the dart/bin while using differ…

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"
 
 #include "bin/lockers.h"
 #include "platform/assert.h"
 
 
 namespace dart {
 namespace bin {
 
 int Process::global_exit_code_ = 0;
 Mutex* Process::global_exit_code_mutex_ = new Mutex();
+Process::ExitHook Process::exit_hook_ = NULL;
 
 void Process::TerminateExitCodeHandler() {
 }
 
 intptr_t Process::CurrentProcessId() {
   UNIMPLEMENTED();
   return 0;
 }
 
 intptr_t Process::SetSignalHandler(intptr_t signal) {
@@ skipping 37 matching lines @@
   UNIMPLEMENTED();
   return -1;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)
 
 #endif  // !defined(DART_IO_DISABLED)