Bug 1623492. Expose OS compositor to telemetry.

Differential Revision: https://phabricator.services.mozilla.com/D67415

--HG--
extra : moz-landing-system : lando

gfx/thebes/gfxPlatform.cpp

@@ -3064,6 +3064,10 @@ void gfxPlatform::InitWebRenderConfig() {
     featureComp.UserEnable("Enabled");
   }
 
+  Telemetry::ScalarSet(
+      Telemetry::ScalarID::GFX_OS_COMPOSITOR,
+      gfx::gfxConfig::IsEnabled(gfx::Feature::WEBRENDER_COMPOSITOR));
+
   // Initialize WebRender partial present config.
   // Partial present is used only when WebRender compositor is not used.
   if (StaticPrefs::gfx_webrender_max_partial_present_rects_AtStartup() > 0) {

toolkit/components/telemetry/Scalars.yaml

@@ -3066,6 +3066,23 @@ gfx:
     record_in_processes:
       - 'main'
     release_channel_collection: opt-out
+  os_compositor:
+    bug_numbers:
+      - 1623492
+    description: >
+      Boolean indicating whether the os compositor is being used by WebRender.
+      Only collected in the first subsession.
+    expires: never
+    kind: boolean
+    notification_emails:
+      - gfx-telemetry-alerts@mozilla.com
+      - jmuizelaar@mozilla.com
+    products:
+      - 'firefox'
+      - 'geckoview'
+    record_in_processes:
+      - 'main'
+    release_channel_collection: opt-out
 
 # The following section contains the form autofill related scalars.
 formautofill: