Bug 1293583 - add test that checks whether the main frame has frame ID 0 r=billm

Tests cannot be run in a new process, so when this test is run along
with other tests, the faulty behavior is not caught.
You can manually check whether the bug is still present by running the
test in isolation:

    mach mochitest browser/components/extensions/test/browser/browser_ext_webNavigation_frameId0.js

MozReview-Commit-ID: LwumSU7zh8R

--HG--
extra : rebase_source : c09fae54cd94af90d7d5391361b33532df6a8d72

browser/components/extensions/test/browser/browser.ini

@@ -77,6 +77,7 @@ support-files =
 [browser_ext_tabs_zoom.js]
 [browser_ext_tabs_update_url.js]
 [browser_ext_topwindowid.js]
+[browser_ext_webNavigation_frameId0.js]
 [browser_ext_webNavigation_getFrames.js]
 [browser_ext_webNavigation_urlbar_transitions.js]
 [browser_ext_windows.js]

browser/components/extensions/test/browser/browser_ext_webNavigation_frameId0.js

@@ -0,0 +1,47 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+add_task(function* webNavigation_getFrameId_of_existing_main_frame() {
+  // Whether the frame ID in the extension API is 0 is determined by a map that
+  // is maintained by |Frames| in ExtensionManagement.jsm. This map is filled
+  // using data from content processes. But if ExtensionManagement.jsm is not
+  // imported, then the "Extension:TopWindowID" message gets lost.
+  // As a result, if the state is not synchronized again, the webNavigation API
+  // will mistakenly report a non-zero frame ID for top-level frames.
+  //
+  // If you want to be absolutely sure that the frame ID is correct, don't open
+  // tabs before starting an extension, or explicitly load the module in the
+  // main process:
+  // Cu.import("resource://gre/modules/ExtensionManagement.jsm", {});
+  //
+  // Or simply run the test again.
+  const BASE = "http://mochi.test:8888/browser/browser/components/extensions/test/browser/";
+  const DUMMY_URL = BASE + "file_dummy.html";
+  let tab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, DUMMY_URL, true);
+
+  function background(DUMMY_URL) {
+    browser.tabs.query({active: true, currentWindow: true}).then(tabs => {
+      return browser.webNavigation.getAllFrames({tabId: tabs[0].id});
+    }).then(frames => {
+      browser.test.assertEq(1, frames.length, "The dummy page has one frame");
+      browser.test.assertEq(0, frames[0].frameId, "Main frame's ID must be 0");
+      browser.test.assertEq(DUMMY_URL, frames[0].url, "Main frame URL must match");
+      browser.test.notifyPass("frameId checked");
+    });
+  }
+
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      "permissions": ["webNavigation"],
+    },
+
+    background: `(${background})(${JSON.stringify(DUMMY_URL)});`,
+  });
+
+  yield extension.startup();
+  yield extension.awaitFinish("frameId checked");
+  yield extension.unload();
+
+  yield BrowserTestUtils.removeTab(tab);
+});