Bug 1689317 - Clipboard events should be composed. r=smaug

Automate some of the copy event tests which tested for this, since there
seems we/WPT don't have a lot of coverage for them.

Differential Revision: https://phabricator.services.mozilla.com/D103428

testing/web-platform/tests/clipboard-apis/events/copy-event.html

@@ -3,11 +3,23 @@
 <link rel="help" href="https://w3c.github.io/clipboard-apis/#clipboard-event-copy">
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
 <div id=log></div>
-<p>Select and copy any part of this text to continue.
+<button id="copy">Trigger copy</button>
+<input id="copyTarget" value="this text should be copied">
 <script>
-setup({explicit_timeout: true});
 async_test(t => {
+  let button = document.getElementById("copy");
+
+  button.addEventListener("click", function(e) {
+    let input = document.getElementById("copyTarget");
+    input.focus();
+    input.select();
+    document.execCommand("copy");
+  });
+
   document.oncopy = t.step_func_done(event => {
     // Nothing can be asserted about the event target until
     // https://github.com/w3c/clipboard-apis/issues/70 is resolved.
@@ -15,5 +27,7 @@ async_test(t => {
     assert_true(event.isTrusted, 'event.isTrusted');
     assert_true(event.composed, 'event.composed');
   });
+
+  test_driver.click(button);
 });
 </script>

widget/BasicEvents.h

@@ -859,6 +859,9 @@ class WidgetEvent : public WidgetEventTime {
    */
   void SetDefaultComposed() {
     switch (mClass) {
+      case eClipboardEventClass:
+        mFlags.mComposed = true;
+        break;
       case eCompositionEventClass:
         mFlags.mComposed =
             mMessage == eCompositionStart || mMessage == eCompositionUpdate ||