VR: Toggle VR mode based on Window Focus.

This helps prevent us from getting into a state where we have a 2D popup
window open but VR mode is on.

Bug: 841814
Change-Id: I280954eb575cf489e10b9307d50e9a862b2b236c
Reviewed-on: https://chromium-review.googlesource.com/1054209
Commit-Queue: Michael Thiessen <mthiesse@chromium.org>
Reviewed-by: Amirhossein Simjour <asimjour@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557608}

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

@@ -577,7 +577,14 @@ public class VrShellImpl
     public void onWindowFocusChanged(boolean focused) {
         // This handles the case where we open 2D popups in 2D-in-VR. We lose window focus, but stay
         // resumed, so we have to listen for focus gain to know when the popup was closed.
-        if (focused) VrShellDelegate.setVrModeEnabled(mActivity, true);
+        // This also handles the case where we're launched via intent and turn VR mode on with
+        // a popup open. We'll lose window focus when the popup 'gets shown' and know to turn VR
+        // mode off.
+        // TODO(asimjour): Focus is a bad signal. We should listen for windows being created and
+        // destroyed if possible.
+        if (VrShellDelegate.getVrClassesWrapper().bootsToVr()) {
+            VrShellDelegate.setVrModeEnabled(mActivity, focused);
+        }
     }
 
     @CalledByNative