Tie VR omnibox to page load progress through TabObserver.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java
index 6e0e596ffc9b1ccc523aff091fac40bdcc7839ac..3e3994026144de1d09a3d555870a53e52f4c6465 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellImpl.java
@@ -239,6 +239,13 @@ public class VrShellImpl extends GvrLayout implements VrShell, SurfaceHolder.Cal
     }
 
     @Override
+    public void onLoadProgressChanged(double progress) {
+        if (mNativeVrShell != 0) {
+            nativeOnLoadProgressChanged(mNativeVrShell, progress);
+        }
+    }
+
+    @Override
     public void shutdown() {
         if (mNativeVrShell != 0) {
             nativeDestroy(mNativeVrShell);
@@ -315,6 +322,7 @@ public class VrShellImpl extends GvrLayout implements VrShell, SurfaceHolder.Cal
     private native void nativeOnTriggerEvent(long nativeVrShell);
     private native void nativeOnPause(long nativeVrShell);
     private native void nativeOnResume(long nativeVrShell);
+    private native void nativeOnLoadProgressChanged(long nativeVrShell, double progress);
     private native void nativeContentPhysicalBoundsChanged(long nativeVrShell, int width,
             int height, float dpr);
     private native void nativeUIPhysicalBoundsChanged(long nativeVrShell, int width, int height,