Make various string_util functions take StringPieces instead of char[].

components/autofill/core/browser/credit_card.cc

Index: components/autofill/core/browser/credit_card.cc
diff --git a/components/autofill/core/browser/credit_card.cc b/components/autofill/core/browser/credit_card.cc
index 10090c5394a77283107c36c344401e7cacc21856..bc9cebf56547879f3c975fa01264a166ecdfc5de 100644
--- a/components/autofill/core/browser/credit_card.cc
+++ b/components/autofill/core/browser/credit_card.cc
@@ -133,9 +133,8 @@ CreditCard::~CreditCard() {}
 
 // static
 const base::string16 CreditCard::StripSeparators(const base::string16& number) {
-  const base::char16 kSeparators[] = {'-', ' ', '\0'};
   base::string16 stripped;
-  base::RemoveChars(number, kSeparators, &stripped);
+  base::RemoveChars(number, base::ASCIIToUTF16("- "), &stripped);
   return stripped;
 }