Enable PaymentRequest on Android by default.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 995e3e1e59cdc552601487ad8664156db08c9b4f..e9a1eb1a55e7a540af35a8516e8a8267f4238332 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1954,6 +1954,11 @@ const FeatureEntry kFeatureEntries[] = {
      ENABLE_DISABLE_VALUE_TYPE(chromeos::switches::kEnableFilesQuickView,
                                chromeos::switches::kDisableFilesQuickView)},
 #endif  // defined(OS_CHROMEOS)
+#if defined(OS_ANDROID)
+    {"enable-payment-request", IDS_FLAGS_ENABLE_PAYMENT_REQUEST_NAME,
+     IDS_FLAGS_ENABLE_PAYMENT_REQUEST_DESCRIPTION, kOsAndroid,
+     FEATURE_VALUE_TYPE(features::kPaymentRequest)},
+#endif  // defined(OS_ANDROID)
     // NOTE: Adding new command-line switches requires adding corresponding
     // entries to enum "LoginCustomFlags" in histograms.xml. See note in
     // histograms.xml and don't forget to run AboutFlagsHistogramTest unit test.