Add missing OFFLINE enum for PluginVm.SetupFailureReason UMA

Bug: 1087726
Change-Id: If56fc0d80ca435e16bc764af49079dd25c6f88e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2362053
Commit-Queue: Timothy Loh <timloh@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Auto-Submit: Timothy Loh <timloh@chromium.org>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799505}

tools/metrics/histograms/enums.xml

@@ -56172,6 +56172,7 @@ Called by update_net_trust_anchors.py.-->
   <int value="22" label="DLC_NEED_SPACE"/>
   <int value="23" label="INSUFFICIENT_DISK_SPACE"/>
   <int value="24" label="INVALID_LICENSE"/>
+  <int value="25" label="OFFLINE"/>
 </enum>
 
 <enum name="PluginVmSetupResult">