Use base::StringPiece for input parameters in Encryptor, rather than std::string

crypto/encryptor.cc

Index: crypto/encryptor.cc
diff --git a/crypto/encryptor.cc b/crypto/encryptor.cc
index 59988f8925ec054a5738339075f94db7bd5dee88..53e88f933f4ef206a044dc3956ed5b3d736b3dc7 100644
--- a/crypto/encryptor.cc
+++ b/crypto/encryptor.cc
@@ -34,7 +34,7 @@ namespace crypto {
 
 /////////////////////////////////////////////////////////////////////////////
 // Encyptor::Counter Implementation.
-Encryptor::Counter::Counter(const std::string& counter) {
+Encryptor::Counter::Counter(const base::StringPiece& counter) {
   CHECK(sizeof(counter_) == counter.length());
 
   memcpy(&counter_, counter.data(), sizeof(counter_));
@@ -70,7 +70,7 @@ size_t Encryptor::Counter::GetLengthInBytes() const {
 /////////////////////////////////////////////////////////////////////////////
 // Partial Encryptor Implementation.
 
-bool Encryptor::SetCounter(const std::string& counter) {
+bool Encryptor::SetCounter(const base::StringPiece& counter) {
   if (mode_ != CTR)
     return false;
   if (counter.length() != 16u)