Add struct traits for base::Value.

base/values.h

 // 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.
 
 // This file specifies a recursive data storage class called Value intended for
 // storing settings and other persistable data.
 //
 // A Value represents something that can be stored in JSON or passed to/from
 // JavaScript. As such, it is NOT a generalized variant type, since only the
 // types supported by JavaScript/JSON are supported.
@@ skipping 70 matching lines @@
   // These methods allow the convenient retrieval of the contents of the Value.
   // If the current object can be converted into the given type, the value is
   // returned through the |out_value| parameter and true is returned;
   // otherwise, false is returned and |out_value| is unchanged.
   virtual bool GetAsBoolean(bool* out_value) const;
   virtual bool GetAsInteger(int* out_value) const;
   virtual bool GetAsDouble(double* out_value) const;
   virtual bool GetAsString(std::string* out_value) const;
   virtual bool GetAsString(string16* out_value) const;
   virtual bool GetAsString(const StringValue** out_value) const;
+  virtual bool GetAsString(StringPiece* out_value) const;
   virtual bool GetAsBinary(const BinaryValue** out_value) const;
   // ListValue::From is the equivalent for std::unique_ptr conversions.
   virtual bool GetAsList(ListValue** out_value);
   virtual bool GetAsList(const ListValue** out_value) const;
   // DictionaryValue::From is the equivalent for std::unique_ptr conversions.
   virtual bool GetAsDictionary(DictionaryValue** out_value);
   virtual bool GetAsDictionary(const DictionaryValue** out_value) const;
   // Note: Do not add more types. See the file-level comment above for why.
 
   // This creates a deep copy of the entire Value tree, and returns a pointer
@@ skipping 58 matching lines @@
   ~StringValue() override;
 
   // Returns |value_| as a pointer or reference.
   std::string* GetString();
   const std::string& GetString() const;
 
   // Overridden from Value:
   bool GetAsString(std::string* out_value) const override;
   bool GetAsString(string16* out_value) const override;
   bool GetAsString(const StringValue** out_value) const override;
+  bool GetAsString(StringPiece* out_value) const override;
   StringValue* DeepCopy() const override;
   bool Equals(const Value* other) const override;
 
  private:
   std::string value_;
 };
 
 class BASE_EXPORT BinaryValue: public Value {
  public:
   // Creates a BinaryValue with a null buffer and size of 0.
@@ skipping 383 matching lines @@
   return out << static_cast<const Value&>(value);
 }
 
 // Stream operator so that enum class Types can be used in log statements.
 BASE_EXPORT std::ostream& operator<<(std::ostream& out,
                                      const Value::Type& type);
 
 }  // namespace base
 
 #endif  // BASE_VALUES_H_