[vr] Fix startup crash on platforms not supporting VR

Bug: 792098
Change-Id: If75e986571a3490c4d70e22a4748e43b517ba857
Reviewed-on: https://chromium-review.googlesource.com/809099Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521821}

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

@@ -335,7 +335,7 @@ public class VrShellDelegate
     public static void maybeRegisterVrEntryHook(final ChromeActivity activity) {
         // Daydream is not supported on pre-N devices.
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.N) return;
-        if (!sChromeStarted) {
+        if (isVrEnabled() && !sChromeStarted) {
             nativeOnChromeStarted();
             sChromeStarted = true;
         }