Remove the debugger_ field from Isolate in a PRODUCT build

runtime/vm/exceptions.cc

Index: runtime/vm/exceptions.cc
diff --git a/runtime/vm/exceptions.cc b/runtime/vm/exceptions.cc
index 343373fa127adef6f5465ce76ed174207d028ef2..cbca706093310e7490bc824b9cc4aad44aeef378 100644
--- a/runtime/vm/exceptions.cc
+++ b/runtime/vm/exceptions.cc
@@ -763,6 +763,7 @@ void Exceptions::Throw(Thread* thread, const Instance& exception) {
   // Do not notify debugger on stack overflow and out of memory exceptions.
   // The VM would crash when the debugger calls back into the VM to
   // get values of variables.
+#if !defined(PRODUCT)
   if (FLAG_support_debugger) {
     Isolate* isolate = thread->isolate();
     if (exception.raw() != isolate->object_store()->out_of_memory() &&
@@ -770,6 +771,7 @@ void Exceptions::Throw(Thread* thread, const Instance& exception) {
       isolate->debugger()->PauseException(exception);
     }
   }
+#endif
   // Null object is a valid exception object.
   ThrowExceptionHelper(thread, exception, StackTrace::Handle(thread->zone()),
                        false);