Tie VR omnibox to page load progress through TabObserver.

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java
index 45a38a74dc7ceb2a1a84a5b1e977f81785ee97dd..8c2608d4ed4d701f43c3d4d69078057db919cfb1 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShell.java
@@ -52,4 +52,9 @@ public interface VrShell {
      * Sets a callback to be run when the close button is tapped.
      */
     void setCloseButtonListener(Runnable runner);
+
+    /**
+     * Handles a change in page load progress.
+     */
+    void onLoadProgressChanged(double progress);
 }