Allow UKM collection of U2F registration/sign request UseCounters

The kU2fCryptotoken{Register,Sign} WebFeature counters record when a
page makes a request to the CryptoToken component extension via the U2F
API in order to register or sign with a security key credential.

Change-Id: I2ea19f46da9028da000e0e5564a7ade242d9d3ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2118851
Auto-Submit: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#753114}

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

@@ -57,6 +57,8 @@ UseCounterPageLoadMetricsObserver::GetAllowedUkmFeatures() {
           WebFeature::kCredentialManagerGetPublicKeyCredential,
           WebFeature::kCredentialManagerMakePublicKeyCredentialSuccess,
           WebFeature::kCredentialManagerGetPublicKeyCredentialSuccess,
+          WebFeature::kU2FCryptotokenRegister,
+          WebFeature::kU2FCryptotokenSign,
           WebFeature::kV8AudioContext_Constructor,
           WebFeature::kElementAttachShadow,
           WebFeature::kElementAttachShadowOpen,