Fix Initializing VrShellImpl can throw a NullPointerException.

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 8e3a6b3baead5999469e0e736a035f05c86fc1d3..b6c4bd450bbbb711d1132cbd013a9cf25fe2e078 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
@@ -409,6 +409,9 @@ public class VrShellDelegate {
     }
 
     private void enterVR() {
+        if (mEnteringVr) {
+            mEnteringVr = false;
+        }
         if (mRestoreSystemUiVisibilityFlag == -1
                 || mActivity.getResources().getConfiguration().orientation
                         != Configuration.ORIENTATION_LANDSCAPE) {
@@ -421,7 +424,6 @@ public class VrShellDelegate {
             });
             return;
         }
-        mEnteringVr = false;
         if (!createVrShell()) {
             if (mRestoreOrientation != null) mActivity.setRequestedOrientation(mRestoreOrientation);
             mRestoreOrientation = null;