Tie VR omnibox to page load progress through TabObserver.

chrome/browser/android/vr_shell/vr_shell.h

Index: chrome/browser/android/vr_shell/vr_shell.h
diff --git a/chrome/browser/android/vr_shell/vr_shell.h b/chrome/browser/android/vr_shell/vr_shell.h
index a95676ea6ce6316c07baf9a73a2cf074ca4cf434..99d2438578c67578196421893ea352cefe6c72a3 100644
--- a/chrome/browser/android/vr_shell/vr_shell.h
+++ b/chrome/browser/android/vr_shell/vr_shell.h
@@ -81,6 +81,9 @@ class VrShell : public device::GvrDelegate, content::WebContentsObserver {
   void SetWebVrMode(JNIEnv* env,
                     const base::android::JavaParamRef<jobject>& obj,
                     bool enabled);
+  void OnLoadProgressChanged(JNIEnv* env,
+                             const base::android::JavaParamRef<jobject>& obj,
+                             double progress);
 
   void ContentWebContentsDestroyed();
   // Called when our WebContents have been hidden. Usually a sign that something