Add Metrics analyzer selection for chromium/src

Depends on first adding Metrics analyzer definition
in service cfg.

The Metrics analyzer recipe has been temporarily changed
to only run for changes by ltina@, https://crrev.com/c/1881935,
so enabling this analyzer is not expected to create comments
on regular CLs.

TBR=tandrii@chromium.org

Bug: 1004564
Change-Id: I008e855b759f97a0e70c400ee7891c7b9fcd2926
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1885015
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Cr-Commit-Position: refs/heads/master@{#710419}

infra/config/generated/tricium-prod.cfg

@@ -24,6 +24,11 @@ selections {
   platform: UBUNTU
 }
 
+selections {
+  function: "Metrics"
+  platform: UBUNTU
+}
+
 selections {
   function: "MojomCommentator"
   platform: UBUNTU

infra/config/tricium-prod.cfg

@@ -24,6 +24,11 @@ selections {
   platform: UBUNTU
 }
 
+selections {
+  function: "Metrics"
+  platform: UBUNTU
+}
+
 selections {
   function: "MojomCommentator"
   platform: UBUNTU