Tie VR omnibox to page load progress through TabObserver.

chrome/browser/android/vr_shell/ui_interface.cc

Index: chrome/browser/android/vr_shell/ui_interface.cc
diff --git a/chrome/browser/android/vr_shell/ui_interface.cc b/chrome/browser/android/vr_shell/ui_interface.cc
index 59e5c459ce5df7b285a333b072590aad36067d1f..6d021b5bf2f876a48614d679880901cc6fa95b7b 100644
--- a/chrome/browser/android/vr_shell/ui_interface.cc
+++ b/chrome/browser/android/vr_shell/ui_interface.cc
@@ -53,6 +53,11 @@ void UiInterface::SetLoading(bool loading) {
   FlushUpdates();
 }
 
+void UiInterface::SetLoadProgress(double progress) {
+  updates_.SetDouble("loadProgress", progress);
+  FlushUpdates();
+}
+
 void UiInterface::SetURL(const GURL& url) {
   std::unique_ptr<base::DictionaryValue> details(new base::DictionaryValue);
   details->SetString("host", url.host());