For #15369: Add documentation for synced tabs metrics.

app/metrics.yaml

@@ -766,6 +766,34 @@ metrics:
     notification_emails:
       - fenix-core@mozilla.com
     expires: "2021-08-01"
+  synced_tabs_opened_count:
+    type: counter
+    lifetime: application
+    description: >
+      A counter that indicates how many synced tabs a user has opened
+    send_in_pings:
+      - metrics
+    bugs:
+      - https://github.com/mozilla-mobile/fenix/issues/15369
+    data_reviews:
+      - https://github.com/mozilla-mobile/fenix/pull/16727
+    notification_emails:
+      - fenix-core@mozilla.com
+    expires: "2021-04-01"
+  has_opened_synced_tabs:
+    type: boolean
+    lifetime: application
+    description: >
+       A boolean that indicates if the user has opened synced tabs
+    send_in_pings:
+      - metrics
+    bugs:
+      - https://github.com/mozilla-mobile/fenix/issues/15369
+    data_reviews:
+      - https://github.com/mozilla-mobile/fenix/pull/16727
+    notification_emails:
+      - fenix-core@mozilla.com
+    expires: "2021-04-01"
   search_count:
     type: labeled_counter
     description: |

docs/metrics.md

@@ -270,12 +270,14 @@ The following metrics are added to the ping:
 | metrics.default_browser |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |Is Fenix the default browser?  |[1](https://github.com/mozilla-mobile/fenix/pull/1067#issuecomment-474598673), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
 | metrics.default_moz_browser |[string](https://mozilla.github.io/glean/book/user/metrics/string.html) |The name of the default browser on device if and only if it's a Mozilla owned product  |[1](https://github.com/mozilla-mobile/fenix/pull/1953/), [2](https://github.com/mozilla-mobile/fenix/pull/5216), [3](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |1, 2 |
 | metrics.has_open_tabs |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |A boolean that indicates if the user has any open NORMAL tabs.  |[1](https://github.com/mozilla-mobile/fenix/pull/12024), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
+| metrics.has_opened_synced_tabs |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |A boolean that indicates if the user has opened synced tabs  |[1](https://github.com/mozilla-mobile/fenix/pull/16727)||2021-04-01 | |
 | metrics.has_recent_pwas |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |A boolean that indicates if the user has recently used PWAs. See recently_used_pwa_count for the actual count.  |[1](https://github.com/mozilla-mobile/fenix/pull/11982#pullrequestreview-437963817), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
 | metrics.has_top_sites |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |A boolean that indicates if the user has top sites  |[1](https://github.com/mozilla-mobile/fenix/pull/9556), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
 | metrics.mozilla_products |[string_list](https://mozilla.github.io/glean/book/user/metrics/string_list.html) |A list of all the Mozilla products installed on device. We currently scan for: Firefox, Firefox Beta, Firefox Aurora, Firefox Nightly, Firefox Fdroid, Firefox Lite, Reference Browser, Reference Browser Debug, Fenix, Focus, and Lockwise.  |[1](https://github.com/mozilla-mobile/fenix/pull/1953/), [2](https://github.com/mozilla-mobile/fenix/pull/5216), [3](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |1, 2 |
 | metrics.recently_used_pwa_count |[counter](https://mozilla.github.io/glean/book/user/metrics/counter.html) |A counter that indicates how many PWAs a user has recently used. Threshold for "recency" set in HomeActivity#PWA_RECENTLY_USED_THRESHOLD. Currently we are not told by the OS when a PWA is removed by the user, so we use the "recently used" heuristic to judge how many PWAs are still active, as a proxy for "installed". This value will only be set if the user has at least *one* recently used PWA. If they have 0, this metric will not be sent, resulting in a null value during analysis on the server-side. To disambiguate between a failed `recently_used_pwa_count` metric and 0 recent PWAs, please see `has_recent_pwas`.  |[1](https://github.com/mozilla-mobile/fenix/pull/11982#pullrequestreview-437963817), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
 | metrics.search_count |[labeled_counter](https://mozilla.github.io/glean/book/user/metrics/labeled_counters.html) |The labels for this counter are `<search-engine-name>.<source>`.  If the search engine is bundled with Fenix `search-engine-name` will be the name of the search engine. If it's a custom search engine (defined: https://github.com/mozilla-mobile/fenix/issues/1607) the value will be `custom`.  `source` will be: `action`, `suggestion`, `widget` or `shortcut` (depending on the source from which the search started). Also added the `other` option for the source but it should never enter on this case.  |[1](https://github.com/mozilla-mobile/fenix/pull/1677), [2](https://github.com/mozilla-mobile/fenix/pull/5216), [3](https://github.com/mozilla-mobile/fenix/pull/7310), [4](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |1, 2 |
 | metrics.search_widget_installed |[boolean](https://mozilla.github.io/glean/book/user/metrics/boolean.html) |Whether or not the search widget is installed  |[1](https://github.com/mozilla-mobile/fenix/pull/10958), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
+| metrics.synced_tabs_opened_count |[counter](https://mozilla.github.io/glean/book/user/metrics/counter.html) |A counter that indicates how many synced tabs a user has opened  |[1](https://github.com/mozilla-mobile/fenix/pull/16727)||2021-04-01 | |
 | metrics.tab_view_setting |[string](https://mozilla.github.io/glean/book/user/metrics/string.html) |A string that indicates the setting for tab view: GRID, LIST  |[1](https://github.com/mozilla-mobile/fenix/pull/15811#issuecomment-706402952)||2021-08-01 |2 |
 | metrics.tabs_open_count |[counter](https://mozilla.github.io/glean/book/user/metrics/counter.html) |A counter that indicates how many NORMAL tabs a user has open. This value will only be set if the user has at least *one* open tab. If they have 0, this ping will not get sent, resulting in a null value. To disambiguate between a failed `tabs_open_count` ping and 0 open tabs, please see `has_open_tabs`.  |[1](https://github.com/mozilla-mobile/fenix/pull/12024), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |
 | metrics.toolbar_position |[string](https://mozilla.github.io/glean/book/user/metrics/string.html) |A string that indicates the new position of the toolbar TOP or BOTTOM  |[1](https://github.com/mozilla-mobile/fenix/pull/6608), [2](https://github.com/mozilla-mobile/fenix/pull/15713#issuecomment-703972068)||2021-08-01 |2 |