Enable PaymentRequest on Android by default.

chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java

Index: chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java b/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java
index 68f471728c4298c8eb57e2e8b55fe0573cd2fad8..76be86c463d456859b8cc8da78d9403c64ecb9fe 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java
@@ -13,6 +13,7 @@ import org.chromium.base.Callback;
 import org.chromium.base.Log;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.R;
+import org.chromium.chrome.browser.ChromeFeatureList;
 import org.chromium.chrome.browser.autofill.PersonalDataManager;
 import org.chromium.chrome.browser.autofill.PersonalDataManager.AutofillProfile;
 import org.chromium.chrome.browser.favicon.FaviconHelper;
@@ -199,6 +200,12 @@ public class PaymentRequestImpl implements PaymentRequest, PaymentRequestUI.Clie
 
         if (mContext == null) {
             disconnectFromClientWithDebugMessage("Web contents don't have associated activity");
+            return;
+        }
+
+        if (!ChromeFeatureList.isEnabled(ChromeFeatureList.WEB_PAYMENTS)) {
+            disconnectFromClientWithDebugMessage(
+                    "Web payments API is disabled", PaymentErrorReason.NOT_SUPPORTED);
         }
     }