Adhere to the Android Payment app spec.

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 789b9f9e71bec3de3a63137bc8311759508c9910..c78df001d3fe7cc3f0f0b81a5c497df7c44f14e2 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
@@ -254,6 +254,7 @@ public class PaymentRequestImpl
     private final String mOriginForDisplay;
     private final String mSchemelessIFrameOriginForPaymentApp;
     private final String mMerchantName;
+    @Nullable
     private final byte[][] mCertificateChain;
     private final AddressEditor mAddressEditor;
     private final CardEditor mCardEditor;
@@ -350,7 +351,7 @@ public class PaymentRequestImpl
     /**
      * Builds the PaymentRequest service implementation.
      *
-     * @param webContents The web contents that have invoked the PaymentRequest API.
+     * @param renderFrameHost The host of the frame that has invoked the PaymentRequest API.
      */
     public PaymentRequestImpl(RenderFrameHost renderFrameHost) {
         assert renderFrameHost != null;