fix render tree triggering when already destroyed (#2547)

Author: patricklx

ember_debug/utils/base-object.js

@@ -6,7 +6,9 @@ export default class BaseObject {
   }
 
   init() {}
-  willDestroy() {}
+  willDestroy() {
+    this.isDestroying = true;
+  }
 
   destroy() {
     this.willDestroy();

ember_debug/view-debug.js

@@ -152,7 +152,7 @@ export default class extends DebugPort {
   }
 
   send() {
-    if (this.isDestroying) {
+    if (this.isDestroying || this.isDestroyed) {
       return;
     }