Bug 1638007 - Replace WebRequest.jsm with ^headers^ in browser_default_image_filename_redirect.js r=mixedpuppy

This test doesn't need to use WebRequest.jsm, so remove the dependency.

Differential Revision: https://phabricator.services.mozilla.com/D77173

toolkit/content/tests/browser/browser.ini

@@ -26,8 +26,6 @@ support-files =
   image.jpg
   image_page.html
   silentAudioTrack.webm
-  doggy.png
-  firebird.png
 
 [browser_autoplay_policy.js]
 support-files =
@@ -109,6 +107,10 @@ run-if = e10s && crashreporter
 [browser_datetime_datepicker.js]
 [browser_default_image_filename.js]
 [browser_default_image_filename_redirect.js]
+support-files =
+  doggy.png
+  firebird.png
+  firebird.png^headers^
 [browser_f7_caret_browsing.js]
 [browser_findbar.js]
 skip-if = os == "linux" && bits == 64 && os_version = "18.04" # Bug 1614739

toolkit/content/tests/browser/browser_default_image_filename_redirect.js

@@ -6,27 +6,12 @@
  * doggy.png in file picker dialog.
  */
 
-let { WebRequest } = ChromeUtils.import(
-  "resource://gre/modules/WebRequest.jsm"
-);
 let MockFilePicker = SpecialPowers.MockFilePicker;
 MockFilePicker.init(window);
 add_task(async function() {
+  // This URL will redirect to doggy.png.
   const URL_FIREBIRD =
     "http://mochi.test:8888/browser/toolkit/content/tests/browser/firebird.png";
-  const URL_DOGGY =
-    "http://mochi.test:8888/browser/toolkit/content/tests/browser/doggy.png";
-  function redirect(requestDetails) {
-    info("Redirecting: " + requestDetails.url);
-    return {
-      redirectUrl: URL_DOGGY,
-    };
-  }
-  WebRequest.onBeforeRequest.addListener(
-    redirect,
-    { urls: new MatchPatternSet(["http://*/*firebird.png"]) },
-    ["blocking"]
-  );
 
   await BrowserTestUtils.withNewTab(URL_FIREBIRD, async function(browser) {
     // Click image to show context menu.
@@ -65,6 +50,4 @@ add_task(async function() {
     contextMenu.hidePopup();
     await popupHiddenPromise;
   });
-
-  WebRequest.onBeforeRequest.removeListener(redirect);
 });

toolkit/content/tests/browser/firebird.png^headers^

@@ -0,0 +1,2 @@
+HTTP 302 Found
+Location: doggy.png