[gamepad] Add GetGamepads to UKM feature list

In an earlier CL, new metrics were added for navigator.getGamepads
when called from a cross-origin subframe or an insecure context
(WebFeature::kGetGamepadsFromCrossOriginSubFrame and
WebFeature::kGetGamepadsFromInsecureContext). This CL enables UKM
for the general case of calling navigator.getGamepads from any
context (WebFeature::kGetGamepads).

BUG=1014608

Change-Id: I276cc1fd23525e4e7ddeb1f3b7f5ea1f48fc387b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863354Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706147}

components/page_load_metrics/browser/observers/use_counter/ukm_features.cc

@@ -139,6 +139,7 @@ UseCounterPageLoadMetricsObserver::GetAllowedUkmFeatures() {
           WebFeature::kHeavyAdIntervention,
           WebFeature::kGetGamepadsFromCrossOriginSubframe,
           WebFeature::kGetGamepadsFromInsecureContext,
+          WebFeature::kGetGamepads,
       }));
   return *opt_in_features;
 }