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

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 7a58ada284ba83ed9c9023d4329ff9547be7b23b..e7a812770fd87db693b8edc079d6379d6d950830 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -90160,6 +90160,7 @@ value.
   <int value="-1473136627" label="enable-web-payments"/>
   <int value="-1467332609" label="tab-management-experiment-type-anise"/>
   <int value="-1460462432" label="disable-media-source"/>
+  <int value="-1456004000" label="VrShell:disabled"/>
   <int value="-1443796945" label="OfflinePagesSharing:disabled"/>
   <int value="-1440152291" label="disable-gesture-typing"/>
   <int value="-1438279809" label="GamepadExtensions:disabled"/>
@@ -90626,6 +90627,7 @@ value.
   <int value="935655516" label="password-import-export:disabled"/>
   <int value="936341613" label="OfflinePagesCT:disabled"/>
   <int value="936919953" label="bypass-app-banner-engagement-checks"/>
+  <int value="938191241" label="VrShell:enabled"/>
   <int value="939554480" label="enable-credit-card-scan"/>
   <int value="939603162" label="BackgroundLoadingForDownloads:disabled"/>
   <int value="943319566" label="enable-intent-picker"/>