Tie VR omnibox to page load progress through TabObserver.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
index 374e6c7804555b8e54f64e3df92f01eb1ae75cc5..7a36bd41bc71ee8959c4815b44dff57685307aaf 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/vr_shell/VrShellDelegate.java
@@ -135,6 +135,12 @@ public class VrShellDelegate {
                     // TODO(mthiesse): Update the native WebContents pointer and compositor.
                     shutdownVR(false, mVrSupportLevel == VR_DAYDREAM /* showTransition */);
                 }
+
+                @Override
+                public void onLoadProgressChanged(Tab tab, int progress) {
+                    if (!mInVr) return;
+                    mVrShell.onLoadProgressChanged((double) progress / 100.0);

[cjgrant, 2017/01/12 19:16:49]

For clarity:
- progress is a double original (WebContents, etc).
- Tab/TabObserver makes it an int for some reason.
- I'm returning it to a double here, as I hope to bypass TabObserver in the
future.

+                }
             };
         }