share content scripts helper function in WebExtensions mochitest

tweak-bug-1207394-test.patch

diff --git a/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html b/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html
--- a/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_web_accessible_resources.html
@@ -18,47 +18,45 @@
 SimpleTest.registerCleanupFunction(() => {
   SpecialPowers.clearUserPref("security.mixed_content.block_display_content");
 });
 
 let image = atob("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAA" +
                  "ACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=");
 const IMAGE_ARRAYBUFFER = Uint8Array.from(image, byte => byte.charCodeAt(0)).buffer;
 
-function contentScriptHelper() {
-  this.testImageLoading = function(src, expectedAction) {
-    let imageLoadingPromise = new Promise((resolve, reject) => {
-      let testImage = document.createElement("img");
-      testImage.setAttribute("src", src);
+function testImageLoading(src, expectedAction) {
+  let imageLoadingPromise = new Promise((resolve, reject) => {
+    let testImage = document.createElement("img");
+    testImage.setAttribute("src", src);
 
-      let loadListener = () => {
-        cleanupListeners();
-        resolve(expectedAction === "loaded");
-      };
+    let loadListener = () => {
+      cleanupListeners();
+      resolve(expectedAction === "loaded");
+    };
 
-      let errorListener = () => {
-        cleanupListeners();
-        resolve(expectedAction === "blocked");
-      };
+    let errorListener = () => {
+      cleanupListeners();
+      resolve(expectedAction === "blocked");
+    };
 
-      let cleanupListeners = () => {
-        testImage.removeEventListener("load", loadListener);
-        testImage.removeEventListener("error", errorListener);
-      }
+    let cleanupListeners = () => {
+      testImage.removeEventListener("load", loadListener);
+      testImage.removeEventListener("error", errorListener);
+    }
 
-      testImage.addEventListener("load", loadListener);
-      testImage.addEventListener("error", errorListener);
+    testImage.addEventListener("load", loadListener);
+    testImage.addEventListener("error", errorListener);
 
-      document.body.appendChild(testImage);
-    });
+    document.body.appendChild(testImage);
+  });
 
-    imageLoadingPromise.then(success => {
-      browser.runtime.sendMessage({name: "image-loading", expectedAction, success});
-    });
-  }
+  imageLoadingPromise.then(success => {
+    browser.runtime.sendMessage({name: "image-loading", expectedAction, success});
+  });
 }
 
 add_task(function* test_web_accessible_resources() {
   function background() {
     let gotURL;
     let tabId;
 
     function loadFrame(url) {
@@ -201,17 +199,17 @@ add_task(function* test_web_accessible_r
   }
 
   function content() {
     browser.runtime.onMessage.addListener(msg => {
       if (msg !== "load-resources") {
         return;
       }
 
-      this.testImageLoading(browser.extension.getURL("image.png"), "loaded");
+      testImageLoading(browser.extension.getURL("image.png"), "loaded");
 
       let testScript = document.createElement("script");
       testScript.setAttribute("src", browser.extension.getURL("test_script.js"));
       document.head.appendChild(testScript);
       browser.runtime.sendMessage("script-loaded");
     });
 
     window.addEventListener("message", function rcv(event) {
@@ -235,17 +233,17 @@ add_task(function* test_web_accessible_r
       }],
       "web_accessible_resources": [
         "image.png",
         "test_script.js",
       ],
     },
     background: `(${background})()`,
     files: {
-      "content_script_helper.js": `(${contentScriptHelper})()`,
+      "content_script_helper.js": `${testImageLoading}`,
       "content_script.js": `(${content})()`,
       "test_script.js": `(${testScript})()`,
       "image.png": IMAGE_ARRAYBUFFER,
     },
   });
 
   // This is used to watch the blocked data bounce off CSP.
   function examiner() {
@@ -300,18 +298,18 @@ add_task(function* test_web_accessible_r
         browser.test.sendMessage(msg);
       }
     });
 
     browser.test.sendMessage("background-ready");
   }
 
   function content() {
-    this.testImageLoading("http://example.com/tests/toolkit/components/extensions/test/mochitest/file_image_bad.png", "blocked");
-    this.testImageLoading(browser.extension.getURL("image.png"), "loaded");
+    testImageLoading("http://example.com/tests/toolkit/components/extensions/test/mochitest/file_image_bad.png", "blocked");
+    testImageLoading(browser.extension.getURL("image.png"), "loaded");
 
     let testScript = document.createElement("script");
     testScript.setAttribute("src", browser.extension.getURL("test_script.js"));
     document.head.appendChild(testScript);
 
     window.addEventListener("message", event => {
       browser.runtime.sendMessage(event.data);
     });
@@ -330,17 +328,17 @@ add_task(function* test_web_accessible_r
       }],
       "web_accessible_resources": [
         "image.png",
         "test_script.js",
       ],
     },
     background: `(${background})()`,
     files: {
-      "content_script_helper.js": `(${contentScriptHelper})()`,
+      "content_script_helper.js": `${testImageLoading}`,
       "content_script.js": `(${content})()`,
       "test_script.js": `(${testScript})()`,
       "image.png": IMAGE_ARRAYBUFFER,
     },
   });
 
   SpecialPowers.setBoolPref("security.mixed_content.block_display_content", true);