Add UseCounter for XrSession.RequestLightProbe

The OT infrastrucutre requires a single UseCounter to measure. This adds
a use counter for RequestLightProbe, which must be gotten before either
of the other Light Estimation API methods can be used.

Bug: 1148871
Change-Id: Ic9ac4b81fca1460497d4ff0753b7ceadcb982dd0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2538132
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Auto-Submit: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827407}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -3057,6 +3057,7 @@ enum WebFeature {
   kMediaStreamTrackGenerator = 3728,
   kMediaStreamTrackProcessor = 3729,
   kAddEventListenerWithAbortSignal = 3730,
+  kXRSessionRequestLightProbe = 3731,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/modules/xr/xr_session.idl

@@ -79,7 +79,7 @@ enum XRReflectionFormat {
   [RuntimeEnabled=WebXRHitTest, CallWith=ScriptState, MeasureAs=XRSessionRequestHitTestSourceForTransientInput, RaisesException]
   Promise<XRTransientInputHitTestSource> requestHitTestSourceForTransientInput(XRTransientInputHitTestOptionsInit options);
 
-  [RuntimeEnabled=WebXRLightEstimation, CallWith=ScriptState, RaisesException]
+  [RuntimeEnabled=WebXRLightEstimation, CallWith=ScriptState, MeasureAs=XRSessionRequestLightProbe, RaisesException]
   Promise<XRLightProbe> requestLightProbe(optional XRLightProbeInit options = {});
 
   [RuntimeEnabled=WebXRImageTracking, CallWith=ScriptState, RaisesException]

tools/metrics/histograms/enums.xml

@@ -30262,6 +30262,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3728" label="MediaStreamTrackGenerator"/>
   <int value="3729" label="MediaStreamTrackProcessor"/>
   <int value="3730" label="AddEventListenerWithAbortSignal"/>
+  <int value="3731" label="XRSessionRequestLightProbe"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">