feat: optimize passing Bytes to Value (#1104)

Now with more move support.

Fixes #1103

Author: devjgm

google/cloud/spanner/bytes.cc

@@ -148,7 +148,7 @@ StatusOr<Bytes> BytesFromBase64(std::string input) {
 }
 
 // Conversion to a base64-encoded US-ASCII `std::string`.
-std::string BytesToBase64(Bytes const& b) { return b.base64_rep_; }
+std::string BytesToBase64(Bytes b) { return std::move(b.base64_rep_); }
 
 }  // namespace internal
 }  // namespace SPANNER_CLIENT_NS

google/cloud/spanner/bytes.h

@@ -32,7 +32,7 @@ class Bytes;  // defined below
 // Internal forward declarations to befriend.
 namespace internal {
 StatusOr<Bytes> BytesFromBase64(std::string input);
-std::string BytesToBase64(Bytes const& b);
+std::string BytesToBase64(Bytes b);
 }  // namespace internal
 
 /**
@@ -79,7 +79,7 @@ class Bytes {
 
  private:
   friend StatusOr<Bytes> internal::BytesFromBase64(std::string input);
-  friend std::string internal::BytesToBase64(Bytes const& b);
+  friend std::string internal::BytesToBase64(Bytes b);
 
   struct Encoder {
     Encoder(std::string& rep) : rep_(rep), len_(0) {}

google/cloud/spanner/value.cc

@@ -232,9 +232,9 @@ google::protobuf::Value Value::MakeValueProto(std::string s) {
   return v;
 }
 
-google::protobuf::Value Value::MakeValueProto(Bytes const& bytes) {
+google::protobuf::Value Value::MakeValueProto(Bytes bytes) {
   google::protobuf::Value v;
-  v.set_string_value(internal::BytesToBase64(bytes));
+  v.set_string_value(internal::BytesToBase64(std::move(bytes)));
   return v;
 }
 

google/cloud/spanner/value.h

@@ -428,7 +428,7 @@ class Value {
   static google::protobuf::Value MakeValueProto(std::int64_t i);
   static google::protobuf::Value MakeValueProto(double d);
   static google::protobuf::Value MakeValueProto(std::string s);
-  static google::protobuf::Value MakeValueProto(Bytes const& b);
+  static google::protobuf::Value MakeValueProto(Bytes b);
   static google::protobuf::Value MakeValueProto(Timestamp ts);
   static google::protobuf::Value MakeValueProto(Date d);
   static google::protobuf::Value MakeValueProto(int i);