[BasicCardDeprecation] Add about flag for basic-card

Add a "enable-payment-request-basic-card" flag to about://flags, enabled
by default. This is to make it easier for developers to test a
environment without the basic-card payment method, in preparation of the
upcoming deprecation.

Bug: 1251421
Change-Id: Id1f56283fe782965505a8c8c11b9b716f630c929
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3170060
Auto-Submit: Liquan (Max) Gu <[email protected]>
Commit-Queue: Rouslan Solomakhin <[email protected]>
Reviewed-by: Rouslan Solomakhin <[email protected]>
Cr-Commit-Position: refs/heads/main@{#923829}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index c25d821..1b11896 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -2756,6 +2756,11 @@
 const char kWebPaymentsExperimentalFeaturesDescription[] =
     "Enable experimental Web Payments API features";
 
+const char kPaymentRequestBasicCardName[] =
+    "PaymentRequest API 'basic-card' method";
+const char kPaymentRequestBasicCardDescription[] =
+    "The 'basic-card' payment method of the PaymentRequest API.";
+
 const char kAppStoreBillingDebugName[] =
     "Web Payments App Store Billing Debug Mode";
 const char kAppStoreBillingDebugDescription[] =