Replace at-/de-tached with dis-connectedCallback

attached() and detached() are Polymer 1 legacy.

Change-Id: Ic86d07bfb95ec316880db261a913004f5a6e5a22
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
index f4772e3..c13092f 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
@@ -114,17 +114,17 @@
   _isScrolling?: boolean;
 
   /** @override */
-  attached() {
-    super.attached();
+  connectedCallback() {
+    super.connectedCallback();
     this.listen(window, 'scroll', '_handleWindowScroll');
   }
 
   /** @override */
-  detached() {
-    super.detached();
+  disconnectedCallback() {
     this.cancelDebouncer(DEBOUNCER_RESET_IS_SCROLLING);
     this.cancel();
     this.unlisten(window, 'scroll', '_handleWindowScroll');
+    super.disconnectedCallback();
   }
 
   _handleWindowScroll() {