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

runtime/bin/process_fuchsia.cc

Index: runtime/bin/process_fuchsia.cc
diff --git a/runtime/bin/process_fuchsia.cc b/runtime/bin/process_fuchsia.cc
index 5858800aba07a18b8f06399ebc2e6ef18fa6337a..cd2f8bfb19147bad98e8689e383383645210260d 100644
--- a/runtime/bin/process_fuchsia.cc
+++ b/runtime/bin/process_fuchsia.cc
@@ -18,6 +18,7 @@ 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() {
 }