Android: Fix a bug in delayed fullscreen operation

This CL fixes a bug in FullscreenManager that handles a pending
fullscreen operation getting active when the tab becomes
user-interactive.

Also added a test that passes when the patch is applied.

Bug: 510282
Change-Id: Id328cc3bd1421de51503bc30a6b4dc5bd91a2c5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298784
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788898}

chrome/android/java/src/org/chromium/chrome/browser/fullscreen/FullscreenHtmlApiHandler.java

@@ -231,13 +231,16 @@ public class FullscreenHtmlApiHandler implements ActivityStateListener, WindowFo
             @Override
             public void onDidFinishNavigation(Tab tab, NavigationHandle navigation) {
                 if (navigation.isInMainFrame() && !navigation.isSameDocument()) {
-                    if (tab == mTab) exitPersistentFullscreenMode();
+                    if (tab == modelSelector.getCurrentTab()) exitPersistentFullscreenMode();
                 }
             }
 
             @Override
             public void onInteractabilityChanged(Tab tab, boolean interactable) {
-                if (!interactable || tab != mTab) return;
+                // Compare |tab| with |TabModelSelector#getCurrentTab()| which is a safer
+                // indicator for the active tab than |mTab|, since the invocation order of
+                // ActivityTabTabObserver and TabModelSelectorTabObserver is not explicitly defined.
+                if (!interactable || tab != modelSelector.getCurrentTab()) return;
                 Runnable enterFullscreen = getEnterFullscreenRunnable(tab);
                 if (enterFullscreen != null) enterFullscreen.run();
             }

chrome/android/javatests/src/org/chromium/chrome/browser/fullscreen/FullscreenManagerTest.java

@@ -44,6 +44,7 @@ import org.chromium.chrome.browser.tab.TabTestUtils;
 import org.chromium.chrome.browser.tab.TabWebContentsDelegateAndroid;
 import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 import org.chromium.chrome.test.ChromeTabbedActivityTestRule;
+import org.chromium.chrome.test.util.ChromeTabUtils;
 import org.chromium.chrome.test.util.FullscreenTestUtils;
 import org.chromium.chrome.test.util.browser.Features;
 import org.chromium.content_public.browser.GestureListenerManager;
@@ -159,6 +160,37 @@ public class FullscreenManagerTest {
                 tab, false, mActivityTestRule.getActivity());
     }
 
+    @Test
+    @MediumTest
+    @Feature({"Fullscreen"})
+    public void testDelayedPersistentFullscreen() {
+        mActivityTestRule.startMainActivityWithURL(LONG_HTML_TEST_PAGE);
+
+        Tab tab = mActivityTestRule.getActivity().getActivityTab();
+        TabWebContentsDelegateAndroid delegate = TabTestUtils.getTabWebContentsDelegate(tab);
+        FullscreenTestUtils.waitForFullscreenFlag(tab, false, mActivityTestRule.getActivity());
+        FullscreenTestUtils.waitForPersistentFullscreen(delegate, false);
+
+        // Open a new tab, which puts the tab to test background.
+        ChromeTabUtils.newTabFromMenu(
+                InstrumentationRegistry.getInstrumentation(), mActivityTestRule.getActivity());
+
+        // Having the background tab enter fullscreen should be delayed until it comes foreground.
+        FullscreenTestUtils.togglePersistentFullscreen(delegate, true);
+        Assert.assertFalse(getPersistentFullscreenMode());
+
+        // Put the tab foreground and assert the fullscreen was entered.
+        ChromeTabUtils.switchTabInCurrentTabModel(mActivityTestRule.getActivity(), tab.getId());
+        Assert.assertEquals(tab, mActivityTestRule.getActivity().getActivityTab());
+        Assert.assertTrue(getPersistentFullscreenMode());
+    }
+
+    private boolean getPersistentFullscreenMode() {
+        return TestThreadUtils.runOnUiThreadBlockingNoException(
+                mActivityTestRule.getActivity()
+                        .getFullscreenManager()::getPersistentFullscreenMode);
+    }
+
     @Test
     @LargeTest
     @Feature({"Fullscreen"})