Adhere to the Android Payment app spec.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentInstrument.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentInstrument.java b/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentInstrument.java
index 53cf5027f51b283bc2af520d5ad95a02646f22cd..952a98e3f0fa80bda7e51e8a2828939d85bc9be8 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentInstrument.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentInstrument.java
@@ -75,9 +75,9 @@ public abstract class PaymentInstrument extends PaymentOption {
      *
      * @param merchantName     The name of the merchant.
      * @param origin           The origin of this merchant.
-     * @param iframeOrigin     The origin of the iframe browsing context that invoked
-     * PaymentRequest.
-     * @param certificateChain The site certificate chain of the merchant.
+     * @param iframeOrigin     The origin of the iframe that invoked PaymentRequest.
+     * @param certificateChain The site certificate chain of the merchant. Can be null for localhost
+     *                         or local file, which are secure contexts without SSL.
      * @param methodDataMap    The payment-method specific data for all applicable payment methods,
      *                         e.g., whether the app should be invoked in test or production, a
      *                         merchant identifier, or a public key.
@@ -87,7 +87,7 @@ public abstract class PaymentInstrument extends PaymentOption {
      * @param callback         The object that will receive the instrument details.
      */
     public abstract void invokePaymentApp(String merchantName, String origin, String iframeOrigin,
-            byte[][] certificateChain, Map<String, PaymentMethodData> methodDataMap,
+            @Nullable byte[][] certificateChain, Map<String, PaymentMethodData> methodDataMap,
             PaymentItem total, List<PaymentItem> displayItems,
             Map<String, PaymentDetailsModifier> modifiers, InstrumentDetailsCallback callback);