Clear callback pointer after using it in AutofillPaymentInstrument.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentInstrument.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentInstrument.java b/chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentInstrument.java
index 682acfee84d655cc4ab2befe179c2182d26ce4e1..aa705adb7d819b84f6e6053ba388ddfb3f41dd1c 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentInstrument.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/payments/AutofillPaymentInstrument.java
@@ -106,7 +106,7 @@ public class AutofillPaymentInstrument
 
             json.endObject();
         } catch (IOException e) {
-            mCallback.onInstrumentDetailsError();
+            onFullCardError();
             return;
         }
 
@@ -120,6 +120,7 @@ public class AutofillPaymentInstrument
     @Override
     public void onFullCardError() {
         mCallback.onInstrumentDetailsError();

[gone, 2016/07/14 17:19:27]

Should this check if mCallback is non null before doing this?

[please use gerrit instead, 2016/07/14 17:31:23]

That can't happen. No need for assert either, because there will be a null
pointer crash on the next line, so we can catch this quickly if some new code
breaks this assumption.

+        mCallback = null;
     }
 
     @Override