Add the c++ code part of bindings2/

sky/engine/bindings2/nullable.h

+// Copyright 2014 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.
+
+#ifndef SKY_ENGINE_BINDINGS2_NULLABLE_H_
+#define SKY_ENGINE_BINDINGS2_NULLABLE_H_
+
+#include "base/logging.h"
+
+namespace blink {
+
+template <typename T>
+class Nullable {
+ public:
+  Nullable() : value_(), is_null_(true) {}
+  Nullable(const T& value) : value_(value), is_null_(false) {}
+  Nullable(const Nullable& other)
+      : value_(other.value_), is_null_(other.is_null_) {}
+
+  Nullable& operator=(const Nullable& other) = default;
+
+  void set(const T& value) {
+    value_ = value;
+    is_null_ = false;
+  }
+
+  const T& get() const {
+    DCHECK(!is_null_);
+    return value_;
+  }
+  T& get() {
+    DCHECK(!is_null_);
+    return value_;
+  }
+
+  bool is_null() const { return is_null_; }
+
+  // See comment in RefPtr.h about what UnspecifiedBoolType is.
+  typedef const T* UnspecifiedBoolType;
+  operator UnspecifiedBoolType() const { return is_null_ ? 0 : &value_; }
+
+  bool operator==(const Nullable& other) const {
+    return (is_null_ && other.is_null_) ||
+           (!is_null_ && !other.is_null_ && value_ == other.value_);
+  }
+
+ private:
+  T value_;
+  bool is_null_;
+};
+
+}  // namespace blink
+
+#endif  // SKY_ENGINE_BINDINGS2_NULLABLE_H_