Remove TabImpl and #getActivity reference from FullscreenHtlmApiHandler

Bug: 952703
Change-Id: I70e46da08c593b4f94d6225cc7cff2f152010da2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2121265Reviewed-by: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754161}

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

@@ -25,7 +25,7 @@ import org.chromium.base.supplier.ObservableSupplierImpl;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.multiwindow.MultiWindowUtils;
 import org.chromium.chrome.browser.tab.Tab;
-import org.chromium.chrome.browser.tab.TabImpl;
+import org.chromium.chrome.browser.tab.TabUtils;
 import org.chromium.content_public.browser.WebContents;
 import org.chromium.ui.widget.Toast;
 
@@ -294,7 +294,7 @@ public class FullscreenHtmlApiHandler {
                 == SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN) {
             systemUiVisibility = applyEnterFullscreenUIFlags(systemUiVisibility);
         } else {
-            Activity activity = ((TabImpl) tab).getActivity();
+            Activity activity = TabUtils.getActivity(tab);
             boolean isMultiWindow = MultiWindowUtils.getInstance().isLegacyMultiWindow(activity)
                     || MultiWindowUtils.getInstance().isInMultiWindowMode(activity);