Add VrShell feature flag and wire it up to VrShell delegate.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index fcf62c7789a206feb64b5d00a978e42fd789d1d7..f38114e3fca399e50269bb161cab4547d899074b 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1033,9 +1033,6 @@ const char kDisableAppLink[] = "disable-app-link";
 // Disables Contextual Search.
 const char kDisableContextualSearch[] = "disable-contextual-search";
 
-// Disable VR UI if supported.
-const char kDisableVrShell[] = "disable-vr-shell";
-
 // Enable the accessibility tab switcher.
 const char kEnableAccessibilityTabSwitcher[] =
     "enable-accessibility-tab-switcher";
@@ -1057,9 +1054,6 @@ const char kEnableHostedMode[] = "enable-hosted-mode";
 // unresponsive web content.
 const char kEnableHungRendererInfoBar[] = "enable-hung-renderer-infobar";
 
-// Enable VR UI if supported.
-const char kEnableVrShell[] = "enable-vr-shell";
-
 // Enables "Add to Home screen" in the app menu to generate WebAPKs.
 const char kEnableWebApk[] = "enable-webapk";