Fix the clicked iframe in two wpt fullscreen tests.

With User Activation v2, activating a parent frame doesn't activate
its subframes.  We fixed these two tests by sending the click to
subframes.  This needed a workaround in auto-click.js because
the mutation observer there in doesn't seem to work when a button
element is added to a subframe.

Bug: 802371
Change-Id: I786668c87b802565e99ad16223cafc8ac1fd6296
Reviewed-on: https://chromium-review.googlesource.com/868323Reviewed-by: Navid Zolghadr <nzolghadr@chromium.org>
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570778}

third_party/WebKit/LayoutTests/external/wpt/fullscreen/api/element-request-fullscreen-and-exit-iframe-manual.html

@@ -37,6 +37,6 @@ async_test(t => {
   document.onfullscreenerror = t.unreached_func('fullscreenerror event');
   iframeDoc.onfullscreenerror = t.unreached_func('iframe fullscreenerror event');
 
-  trusted_request(t, iframeBody, document.body);
+  trusted_request(t, iframeBody, iframeBody);
 });
 </script>

third_party/WebKit/LayoutTests/external/wpt/fullscreen/model/move-to-fullscreen-iframe-manual.html

@@ -10,7 +10,7 @@ async_test(t => {
   const iframeDoc = iframe.contentDocument;
 
   // Enter fullscreen for the iframe's body element.
-  trusted_request(t, iframeDoc.body, document.body);
+  trusted_request(t, iframeDoc.body, iframeDoc.body);
   document.onfullscreenchange = t.step_func(() => {
     assert_equals(document.fullscreenElement, iframe, "document's initial fullscreen element");
     assert_equals(iframeDoc.fullscreenElement, iframeDoc.body, "iframe's initial fullscreen element");

third_party/WebKit/LayoutTests/external/wpt_automation/fullscreen/auto-click.js

@@ -40,10 +40,19 @@ function observe(target) {
   observer.observe(target, { childList: true, subtree: true });
 }
 
-// Handle what's already in the document.
+// Handle what's already in the document and subframes.
 for (const button of document.getElementsByTagName('button')) {
   click(button);
 }
+for (const iframe of document.getElementsByTagName('iframe')) {
+  if (!iframe.contentDocument)
+    continue;
+  for (const button of iframe.contentDocument.getElementsByTagName('button'))
+    click(button);
+}
+
+// Observe future changes in the document and subframes.
+observe(document);
 for (const iframe of document.getElementsByTagName('iframe')) {
   if (iframe.contentDocument)
     observe(iframe.contentDocument);
@@ -53,7 +62,4 @@ for (const iframe of document.getElementsByTagName('iframe')) {
   });
 }
 
-// Observe future changes.
-observe(document);
-
 })();