arc: Prepare ArcAuthEndpoint flag for finch experiment.

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 2238177d7acc07dcf276eca1c0bf75c2fa7252f8..623cd45c0aeb22f60c8aa0c9278a339fa8a075e3 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91100,6 +91100,7 @@ value.
   <int value="-1559789642" label="RunAllFlashInAllowMode:enabled"/>
   <int value="-1553477903" label="ash-disable-text-filtering-in-overview-mode"/>
   <int value="-1546903171" label="enable-touch-drag-drop"/>
+  <int value="-1544248549" label="ArcUseAuthEndpoint:enabled"/>
   <int value="-1543316040"
       label="DisplayPersistenceToggleInPermissionPrompts:disabled"/>
   <int value="-1536293422" label="SharedArrayBuffer:enabled"/>
@@ -91222,6 +91223,7 @@ value.
   <int value="-979034258" label="disable-ntp-other-sessions-menu"/>
   <int value="-978700508" label="disable-simplified-fullscreen-ui"/>
   <int value="-977476498" label="disable-eol-notification"/>
+  <int value="-972737445" label="ArcUseAuthEndpoint:disabled"/>
   <int value="-972425050" label="gesture-editing"/>
   <int value="-968010468" label="SharedArrayBuffer:disabled"/>
   <int value="-964676765" label="enable-accelerated-mjpeg-decode"/>