Remove usages of deprecated toolbar methods from CarHTMLViewer

Bug: 187078438
Test: Manually
Change-Id: I9de578d61bc7f9c250bad81079bcb9981b8c980e

src/com/android/htmlviewer/CarHTMLViewerActivity.java

diff --git a/src/com/android/htmlviewer/CarHTMLViewerActivity.java b/src/com/android/htmlviewer/CarHTMLViewerActivity.java
index de31bff..465fca5 100644
--- a/src/com/android/htmlviewer/CarHTMLViewerActivity.java
+++ b/src/com/android/htmlviewer/CarHTMLViewerActivity.java
@@ -19,7 +19,7 @@
 import android.webkit.WebView;
 
 import com.android.car.ui.core.CarUi;
-import com.android.car.ui.toolbar.Toolbar;
+import com.android.car.ui.toolbar.NavButtonMode;
 import com.android.car.ui.toolbar.ToolbarController;
 
 /**
@@ -34,7 +34,7 @@
         WebView webView = requireViewById(R.id.webview);
         webView.setDefaultFocusHighlightEnabled(false);
         mToolbar = CarUi.requireToolbar(this);
-        mToolbar.setState(Toolbar.State.SUBPAGE);
+        mToolbar.setNavButtonMode(NavButtonMode.BACK);
     }
 
     @Override