[headless] Deflake requestFullscreen call tests

Race between fullscreen change and frame resized notifications
caused test flakiness.

This CL stabilizes the test by waiting for the racy events using
Promise.all().

Bug: 339788212, 335520870
Change-Id: I3ca12da9edea018e45d4437b5119512ee2a2a59b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5533640
Auto-Submit: Peter Kvitek <kvitekp@chromium.org>
Commit-Queue: Peter Kvitek <kvitekp@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1300343}

headless/test/data/protocol/sanity/request-fullscreen-expected.txt

@@ -1,2 +1,3 @@
 Tests element requestFullscreen.
-Entered fullscreen mode: fullscreen-div
+Seen page zoom and fullscreen element: fullscreen-div
+Seen page un-zoom

headless/test/data/protocol/sanity/request-fullscreen.js

@@ -8,44 +8,40 @@
         <div id="fullscreen-div">The element.</div>
       </body>
       <script>
-        function toggleFullscreen() {
+        function enterFullscreen() {
           const element = document.getElementById("fullscreen-div");
-          if (!document.fullscreenElement) {
+          return new Promise(resolve => {
+            element.addEventListener("fullscreenchange", () => {
+              if (document.fullscreenElement) {
+                resolve(document.fullscreenElement.id);
+              }
+            });
             element.requestFullscreen();
-          } else {
-            document.exitFullscreen();
           }
-        }
+        )}
 
-        function fullscreenchanged(event) {
-          if (document.fullscreenElement) {
-            console.log("Entered fullscreen mode: "
-                + document.fullscreenElement.id);
-          }
+        function exitFullscreen() {
+          document.exitFullscreen();
         }
-
-        document.getElementById("fullscreen-div")
-          .addEventListener("fullscreenchange", fullscreenchanged);
       </script>
       </html>
   `;
   const {session, dp} =
       await testRunner.startHTML(html, 'Tests element requestFullscreen.');
 
-  await dp.Runtime.enable();
-
-  dp.Runtime.onConsoleAPICalled(data => {
-    const text = data.params.args[0].value;
-    testRunner.log(text);
-  });
-
   await dp.Page.enable();
 
-  session.evaluateAsyncWithUserGesture('window.toggleFullscreen();');
-  await dp.Page.onceFrameResized();
+  const [entered_fullscreen] = await Promise.all([
+    session.evaluateAsyncWithUserGesture('window.enterFullscreen();'),
+    dp.Page.onceFrameResized()
+  ]);
 
-  session.evaluateAsyncWithUserGesture('window.toggleFullscreen();');
+  testRunner.log(
+      'Seen page zoom and fullscreen element: ' + entered_fullscreen);
+
+  session.evaluateAsyncWithUserGesture('window.exitFullscreen();');
   await dp.Page.onceFrameResized();
+  testRunner.log('Seen page un-zoom');
 
   testRunner.completeTest();
 })

headless/test/headless_protocol_browsertest.cc

@@ -370,13 +370,7 @@ HEADLESS_PROTOCOL_TEST(LargeBrowserWindowSize,
 HEADLESS_PROTOCOL_TEST(ScreencastBasics, "sanity/screencast-basics.js")
 HEADLESS_PROTOCOL_TEST(ScreencastViewport, "sanity/screencast-viewport.js")
 
-// https://crbug.com/339788212
-#if BUILDFLAG(IS_MAC)
-#define MAYBE_RequestFullscreen DISABLED_RequestFullscreen
-#else
-#define MAYBE_RequestFullscreen RequestFullscreen
-#endif
-HEADLESS_PROTOCOL_TEST(MAYBE_RequestFullscreen, "sanity/request-fullscreen.js")
+HEADLESS_PROTOCOL_TEST(RequestFullscreen, "sanity/request-fullscreen.js")
 
 class HeadlessProtocolBrowserTestWithProxy
     : public HeadlessProtocolBrowserTest {