Add necessary support functions so that embedders can implemented pause on start and exit

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index ee0404b2e1c1317975f45714160cab2cf5b3edc3..e6ccc6b2a94f6c44e6f2614c60e9d194ec86b4a3 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -298,6 +298,14 @@ class Isolate : public BaseIsolate {
   bool is_runnable() const { return is_runnable_; }
   void set_is_runnable(bool value) { is_runnable_ = value; }
 
+  bool pause_isolates_flags_overridden() const {
+    return pause_isolates_flags_overridden_;
+  }
+
+  void set_pause_isolates_flags_overridden(bool value) {
+    pause_isolates_flags_overridden_ = value;
+  }
+
   IsolateSpawnState* spawn_state() const { return spawn_state_; }
   void set_spawn_state(IsolateSpawnState* value) { spawn_state_ = value; }
 
@@ -749,6 +757,7 @@ class Isolate : public BaseIsolate {
   MessageHandler* message_handler_;
   IsolateSpawnState* spawn_state_;
   bool is_runnable_;
+  bool pause_isolates_flags_overridden_;
   Dart_GcPrologueCallback gc_prologue_callback_;
   Dart_GcEpilogueCallback gc_epilogue_callback_;
   intptr_t defer_finalization_count_;