Remove some non-essential StringPiece->std::string conversion in base/

base/json/json_parser.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/json/json_parser.h"
 
 #include <cmath>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 133 matching lines @@
 
   // Overridden from Value:
   bool GetAsString(std::string* out_value) const override {
     string_piece_.CopyToString(out_value);
     return true;
   }
   bool GetAsString(string16* out_value) const override {
     *out_value = UTF8ToUTF16(string_piece_);
     return true;
   }
-  Value* DeepCopy() const override {
-    return new StringValue(string_piece_.as_string());
-  }
+  Value* DeepCopy() const override { return new StringValue(string_piece_); }
   bool Equals(const Value* other) const override {
     std::string other_string;
     return other->IsType(TYPE_STRING) && other->GetAsString(&other_string) &&
         StringPiece(other_string) == string_piece_;
   }
 
  private:
   // The location in the original input stream.
   StringPiece string_piece_;
 
@@ skipping 814 matching lines @@
                                            const std::string& description) {
   if (line || column) {
     return StringPrintf("Line: %i, column: %i, %s",
         line, column, description.c_str());
   }
   return description;
 }
 
 }  // namespace internal
 }  // namespace base