[Coverity] Change some pass by values to pass by const refs.

chrome/browser/webdata/autofill_change.h

Index: chrome/browser/webdata/autofill_change.h
diff --git a/chrome/browser/webdata/autofill_change.h b/chrome/browser/webdata/autofill_change.h
index 297a6a79f678812ee2cb1124829a5fa4cf1ce9e5..079a94a3218e65685106b4d4826df15e991b2baa 100644
--- a/chrome/browser/webdata/autofill_change.h
+++ b/chrome/browser/webdata/autofill_change.h
@@ -54,7 +54,7 @@ class AutofillProfileChange : public GenericAutofillChange<std::string> {
   // When |type| == UPDATE, |profile| should be non-NULL.
   // When |type| == REMOVE, |profile| should be NULL.
   AutofillProfileChange(Type type,
-                        std::string key,
+                        const std::string& key,
                         const AutofillProfile* profile);
   virtual ~AutofillProfileChange();
 
@@ -75,7 +75,7 @@ class AutofillCreditCardChange : public GenericAutofillChange<std::string> {
   // When |type| == UPDATE, |credit_card| should be non-NULL.
   // When |type| == REMOVE, |credit_card| should be NULL.
   AutofillCreditCardChange(Type type,
-                           std::string key,
+                           const std::string& key,
                            const CreditCard* credit_card);
   virtual ~AutofillCreditCardChange();