[vr] Show toast in 2D-in-VR telling user that Chrome is getting ready

This toast is shown if the VR module is not installed yet when launching
Chrome on standalone VR headsets.

Bug: 914498
Change-Id: Iaac05f06e20a40d62dca52916bb158914edb4320
Reviewed-on: https://chromium-review.googlesource.com/c/1393556Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619684}

chrome/android/java/src/org/chromium/chrome/browser/vr/VrDelegateFallback.java

@@ -17,7 +17,9 @@ import org.chromium.base.Log;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.compat.ApiHelperForN;
 import org.chromium.base.library_loader.LibraryLoader;
+import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ChromeActivity;
+import org.chromium.ui.widget.Toast;
 
 /**
  * Fallback {@link VrDelegate} implementation if the VR module is not available.
@@ -202,6 +204,9 @@ import org.chromium.chrome.browser.ChromeActivity;
             }
             // Set up 2D-in-VR.
             removeBlackOverlayView(activity, false);
+            Toast.makeText(ContextUtils.getApplicationContext(),
+                         R.string.vr_preparing_vr_toast_standalone_text, Toast.LENGTH_SHORT)
+                    .show();
         } else {
             activity.finish();
         }

chrome/android/java/strings/android_chrome_strings.grd

@@ -3721,6 +3721,9 @@ However, you aren’t invisible. Going private doesn’t hide your browsing from
       <message name="IDS_VR_MODULE_INSTALL_FAILURE_TEXT" desc="Text shown on a toast when Chrome failed to install the VR dynamic feature module.">
         Failed to install VR module
       </message>
+      <message name="IDS_VR_PREPARING_VR_TOAST_STANDALONE_TEXT" desc="Text shown on a toast when Chrome's VR browser could not be started due to the VR module missing.">
+        Chrome is still preparing for VR. Restart Chrome later.
+      </message>
 
       <if expr="enable_arcore">
         <!-- ARCore check infobar -->