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

runtime/bin/process_linux.cc

Index: runtime/bin/process_linux.cc
diff --git a/runtime/bin/process_linux.cc b/runtime/bin/process_linux.cc
index e533cc50d6583ed60d7c90d8bc1cfc1575584f54..fff03f9a258f167c77f7aae39236fe806d71aca7 100644
--- a/runtime/bin/process_linux.cc
+++ b/runtime/bin/process_linux.cc
@@ -34,6 +34,7 @@ namespace bin {
 
 int Process::global_exit_code_ = 0;
 Mutex* Process::global_exit_code_mutex_ = new Mutex();
+Process::ExitHook Process::exit_hook_ = NULL;
 
 // ProcessInfo is used to map a process id to the file descriptor for
 // the pipe used to communicate the exit code of the process to Dart.