Deal with frame removal by content scripts

chrome/test/data/extensions/api_test/executescript/destructive/remove_self.js

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+if (top === window) {
+  testTop();
+} else {
+  testChild();
+}
+
+function testTop() {
+  var testMessage = {};
+  function reportFrames() {
+    if (reportFrames.didRun)
+      return;
+    reportFrames.didRun = true;
+    testMessage.frameCount = frames.length;
+    testMessage.frameHTML = window.frameHTML;
+    chrome.runtime.sendMessage(testMessage);
+  }
+  window.onmessage = function(event) {
+    if (event.data === 'toBeRemoved')

[Devlin, 2016/03/15 16:34:34]

Do we expect any other messages?  Can this be an assert?

[robwu, 2016/03/16 22:03:32]

Done.

+      reportFrames();
+  };
+  window.onload = function() {
+    // Fall back, in case the content script never ran.

[Devlin, 2016/03/15 16:34:35]

If the content script never runs, shouldn't this be a failure?  Or at least an
asynchronous post to reportFrames?  I'd like to avoid a magic 3 second timeout.

[robwu, 2016/03/16 22:03:32]

This event was too defensive and is not necessary.
If the message never arrives due to some bug, then the test will time out and
someone will spawn a bug report.

+    setTimeout(reportFrames, 3000);
+  };
+
+  if (window.frameHTML) {  // Set by child frame...
+    // about:blank frames are synchronously parsed, so their document_end script
+    // injection happens before the main frame's injection.
+    var expectChildBeforeMain = location.search.includes('?blankend');
+    if (!expectChildBeforeMain) {
+      // Add a message to the test notification to cause the test to fail,
+      // with some useful information for diagnostics.
+      testMessage.warning = 'Content script in child frame was executed ' +
+        'before the main frame\'s content script!';

[Devlin, 2016/03/15 00:53:32]

nit: indentation

[robwu, 2016/03/16 22:03:32]

Done.

+    }
+    reportFrames();
+  }
+  window.frameHTML = '(not set)';
+}
+
+function testChild() {
+  var TEST_HOST = parent.location.hostname;
+
+  if (TEST_HOST === 'synchronous') {
+    doRemove();
+  } else if (TEST_HOST === 'microtask') {
+    Promise.resolve().then(doRemove);
+  } else if (TEST_HOST === 'macrotask') {
+    setTimeout(doRemove, 0);
+  } else if (TEST_HOST.startsWith('domnodeinserted')) {
+    removeOnEvent('DOMNodeInserted');
+  } else if (TEST_HOST.startsWith('domsubtreemodified')) {
+    removeOnEvent('DOMSubtreeModified');
+  } else {
+    console.error('Unexpected test: ' + TEST_HOST);
+    chrome.test.fail();
+  }
+
+  function doRemove() {
+    parent.frameHTML = document.documentElement.outerHTML || '(no outerHTML)';
+    parent.postMessage('toBeRemoved', '*');
+    // frameElement = <iframe> element in parent document.
+    frameElement.remove();
+  }
+
+  function removeOnEvent(eventName) {
+    // For document_start scripts, DOM mutation events are likely, so pick a
+    // generous time-out delay to make sure that all parser-initiated DOM
+    // mutations have been processed.
+    // DOM mutation events are not really expected in document_end scripts, so
+    // use a very small time-out delay.
+    var delay = parent.location.search.includes('?start') ? 1000 : 50;
+    var expected = parseInt(TEST_HOST.match(/\d+/)[0]);
+    // Fallback in case the mutation events are not triggered.
+    setTimeout(function() {
+      if (expected > 0) {
+        expected = 0;
+        doRemove();

[Devlin, 2016/03/15 16:34:34]

I'm not quite sure I understand the reasoning here.  We wait for n event
firings, but if we don't see n events, we just go ahead anyway?  I'd prefer a
more deterministic test where we can wait for one specific thing, rather than "n
or some time, whichever happens first".  If we don't expect n events to occur,
we don't need that test, right?  (e.g., if we have a test for 2 events and 3
events, but we only ever get 2 events, the 3 event test is just a dup of the 2
event test.)

[robwu, 2016/03/16 22:03:32]

I replaced the timer with a window.onload notification.

+      }
+    }, delay);
+    document.addEventListener(eventName, function() {
+      if (--expected === 0)
+        doRemove();
+    });
+  }
+}