PSA: Re-adding Credential.isConditionalMediationAvailable() to the Credential interface

[Mohamed Amir Yosef]

  Hi everyone,

  This is a quick PSA to let you know that we are restoring the isConditionalMediationAvailable() static method to the base Credential interface.

  Background:
  Credential.isConditionalMediationAvailable() was originally approved in this Intent to Ship [1]. However, when conditional mediation was shipped for PublicKeyCredential [2],
  the method was accidentally removed from the base Credential interface in this CL [3].

  This removal caused failures in some Web Platform Tests (WPTs) that expect the method to be present on the base Credential interface, as dictated by the
  Credential Management spec [4].

  What is changing:
  To fix these test failures and align with the specification, we are landing a fix (CL 7663697) [5] that:
   1. Re-adds isConditionalMediationAvailable() to the base Credential IDL.
   2. Implements a default behavior in Credential that returns false.
   3. Maintains the specialized implementation in PublicKeyCredential that queries the authenticator for WebAuthn-specific support.

  Since this is simply restoring a previously approved API that disappeared by mistake, no new API approvals or Intent to Ship are required. This email serves as a record for the
  history books.

  Please let me know if you have any questions!

  Thanks,
  Mohamed

  Links:
  [1] Original Approval: https://groups.google.com/a/chromium.org/g/blink-dev/c/7ouLjWzcjb0/m/gdHNpAhgBwAJ
  [2] PublicKeyCredential I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/gB4yAmF4msE/m/NfaPLNkcAgAJ
  [3] CL where it accidentally disappeared: https://crrev.com/c/3792649
  [4] Credential Management Spec: https://www.w3.org/TR/credential-management-1/#the-credential-interface
  [5] Current Fix CL: https://crrev.com/c/7663697