crostini: Terminal launch metrics cover until vsh bind

Instead of reporting success/failure after launching Crostini, report
them after binding into the container so we have coverage of the full
flow. Unlike the previous attempt which was reverted due to destroying
a weak pointer cross-sequence, startup_status is now a member of
TerminalPrivateOpenTerminalProcessFunction so it gets created and
destroyed on the UI thread.

Bug: 1188992
Test: Browser tests, deploy and check histograms
Change-Id: Ie25146ff54ea348653e34d6f5d0530809432173d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2843145
Reviewed-by: Joel Hockey <joelhockey@chromium.org>
Commit-Queue: David Munro <davidmunro@google.com>
Cr-Commit-Position: refs/heads/master@{#875456}
GitOrigin-RevId: 0ba5b9a678be211583a19cc0caf58fd215207fe0
diff --git a/metrics/histograms/enums.xml b/metrics/histograms/enums.xml
index ec2b974..ac916f6 100644
--- a/metrics/histograms/enums.xml
+++ b/metrics/histograms/enums.xml
@@ -15653,6 +15653,7 @@
   <int value="62" label="NEED_UPDATE"/>
   <int value="63" label="SHARE_PATHS_FAILED"/>
   <int value="64" label="UNREGISTERED_APPLICATION"/>
+  <int value="65" label="VSH_CONNECT_FAILED"/>
 </enum>
 
 <enum name="CrostiniSettingsEvent">