weblayer: adds test for top-view crash

BUG=1075662
TEST=FullscreenCallbackTest.testDestroyFragmentWhileFullscreen

Change-Id: I46cc5865fe5b395304f860d715704bc909a818ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2170976Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763492}

weblayer/browser/android/javatests/src/org/chromium/weblayer/test/FullscreenCallbackTest.java

@@ -79,4 +79,13 @@ public class FullscreenCallbackTest {
         mDelegate.waitForExitFullscreen();
         Assert.assertEquals(1, mDelegate.mExitFullscreenCount);
     }
+
+    /**
+     * Verifies there are no crashes when destroying the fragment in fullscreen.
+     */
+    @Test
+    @SmallTest
+    public void testDestroyFragmentWhileFullscreen() {
+        TestThreadUtils.runOnUiThreadBlocking(() -> { mActivity.destroyFragment(); });
+    }
 }

weblayer/shell/android/shell_apk/src/org/chromium/weblayer/shell/InstrumentationActivity.java

@@ -91,6 +91,21 @@ public class InstrumentationActivity extends FragmentActivity {
         return mBrowser;
     }
 
+    /**
+     * Explicitly destroys the fragment. There is normally no need to call this. It's useful for
+     * tests that want to verify destruction.
+     */
+    public void destroyFragment() {
+        removeCallbacks();
+
+        FragmentManager fragmentManager = getSupportFragmentManager();
+        FragmentTransaction transaction = fragmentManager.beginTransaction();
+        transaction.remove(mFragment);
+        transaction.commitNow();
+        mFragment = null;
+        mBrowser = null;
+    }
+
     /** Interface used to intercept intents for testing. */
     public static interface IntentInterceptor {
         void interceptIntent(Fragment fragment, Intent intent, int requestCode, Bundle options);
@@ -194,12 +209,17 @@ public class InstrumentationActivity extends FragmentActivity {
     @Override
     protected void onDestroy() {
         super.onDestroy();
+        removeCallbacks();
+    }
+
+    private void removeCallbacks() {
         if (mTabCallback != null) {
             mTab.unregisterTabCallback(mTabCallback);
             mTabCallback = null;
         }
         if (mTabListCallback != null) {
             mBrowser.unregisterTabListCallback(mTabListCallback);
+            mTabListCallback = null;
         }
     }