Clean up VR Shell mode transitions (and fix potential webvr startup race).

chrome/browser/android/vr_shell/vr_shell.h

Index: chrome/browser/android/vr_shell/vr_shell.h
diff --git a/chrome/browser/android/vr_shell/vr_shell.h b/chrome/browser/android/vr_shell/vr_shell.h
index 322b1b1e7e7542039b03260b0f93b1fcc3fc5f5e..7c1941146e25a8a11ef899f3b620a829ec3efd35 100644
--- a/chrome/browser/android/vr_shell/vr_shell.h
+++ b/chrome/browser/android/vr_shell/vr_shell.h
@@ -61,7 +61,8 @@ class VrShell : public device::GvrDelegate, content::WebContentsObserver {
           content::WebContents* main_contents,
           ui::WindowAndroid* content_window,
           content::WebContents* ui_contents,
-          ui::WindowAndroid* ui_window);
+          ui::WindowAndroid* ui_window,
+          bool for_web_vr);
 
   void UpdateCompositorLayers(JNIEnv* env,
                               const base::android::JavaParamRef<jobject>& obj);
@@ -196,8 +197,6 @@ class VrShell : public device::GvrDelegate, content::WebContentsObserver {
   int content_tex_height_ = 0;
   gvr::Sizei content_tex_pixels_for_webvr_ = {0, 0};
 
-  bool webvr_mode_ = false;
-
   // The pose ring buffer size must be a power of two to avoid glitches when
   // the pose index wraps around. It should be large enough to handle the
   // current backlog of poses which is 2-3 frames.