Add some delay before updating the DOM with search results.

This change improves the performance in Chromium when the <input> has only one
or two letters.

lib/ffdocs/view/javascript/search.js

@@ -4,7 +4,14 @@ class SearchInput {
     this.prefetchLinks = new Set();
 
     elem.addEventListener("input", () => {
-      this.update(elem.value.trim().toLowerCase());
+      const query = elem.value.trim().toLowerCase();
+      const delay = query.length < 3 ? 300 : 50;
+
+      if (this.timerAfterInput !== undefined) {
+        clearTimeout(this.timerAfterInput);
+      }
+
+      this.timerAfterInput = setTimeout(() => this.update(query), delay);
     });
 
     elem.addEventListener("keydown", (event) => {