Fix a clipboard error in Vimium iframes in Chrome

Using link hints or copyCurrentUrl while the help dialog is showing triggered this error
in Chrome. The extension got into a bad state on the page and required a refresh:

Potential permissions policy violation: clipboard-read is not allowed in this
document.

Author: philc

content_scripts/hud.js

@@ -47,12 +47,6 @@ const HUD = {
         "vimium-hud-frame",
         this.handleUIComponentMessage.bind(this),
       );
-      // Allow to access to the clipboard through iframes.
-      // This is only valid/necessary for Chrome. Firefox will show this console warning:
-      // 'Feature Policy: Skipping unsupported feature name "clipboard-read"'
-      if (!Utils.isFirefox()) {
-        this.hudUI.iframeElement.allow = "clipboard-read; clipboard-write";
-      }
     }
     // this[data.name]? data
     if (this.tween == null) {

content_scripts/ui_component.js

@@ -32,6 +32,16 @@ class UIComponent {
     const isDomTests = iframeUrl.includes("?dom_tests=true");
     this.iframeElement = DomUtils.createElement("iframe");
 
+    // Allow Vimium's iframes to have clipboard access in Chrome. This is needed when triggering
+    // some commands, like link hints or copyCurrentUrl, from within the help dialog. Firefox does
+    // not support clipboard-read and clipboard-write in the allow attribute. NOTE(philc): this
+    // permission has to be set before we append the iframe to the DOM, or Chrome will log the
+    // console error "Potential permissions policy violation: clipboard-read is not allowed in this
+    // document."
+    if (!Utils.isFirefox()) {
+      this.iframeElement.allow = "clipboard-read; clipboard-write";
+    }
+
     const styleSheet = DomUtils.createElement("style");
     styleSheet.type = "text/css";
     // Default to everything hidden while the stylesheet loads.

tests/unit_tests/ui_component_test.js

@@ -1,4 +1,5 @@
 import * as testHelper from "./test_helper.js";
+import "../../lib/utils.js";
 import "../../lib/dom_utils.js";
 import "../../content_scripts/ui_component.js";
 
@@ -17,6 +18,7 @@ context("UIComponent", () => {
   setup(async () => {
     // Which page we load doesn't matter; we just need any DOM.
     await testHelper.jsdomStub("pages/help_dialog_page.html");
+    stub(Utils, "isFirefox", () => false);
   });
 
   teardown(() => {