VR: Don't stay in VR when exiting webVR if the activity doesn't support VR browsing.

BUG=718610

Review-Url: https://codereview.chromium.org/2862993002
Cr-Commit-Position: refs/heads/master@{#469525}

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

@@ -614,7 +614,7 @@ public class VrShellDelegate implements ApplicationStatus.ActivityStateListener,
     private boolean exitWebVRPresent() {
         if (!mInVr) return false;
         mVrShell.setWebVrModeEnabled(false);
-        if (!isVrShellEnabled(mVrSupportLevel)) {
+        if (!isVrShellEnabled(mVrSupportLevel) || !activitySupportsVrBrowsing(mActivity)) {
             shutdownVr(false /* isPausing */, true /* showTransition */);
         }
         return true;