Import Dart bindings as of Blink r188698. This merely copies the files over and does not attach any…

sky/engine/bindings-dart/common/Nullable.h

Index: sky/engine/bindings-dart/common/Nullable.h
diff --git a/sky/engine/bindings/core/v8/Nullable.h b/sky/engine/bindings-dart/common/Nullable.h
similarity index 85%
copy from sky/engine/bindings/core/v8/Nullable.h
copy to sky/engine/bindings-dart/common/Nullable.h
index bed146b405a02fb17bbdd4c88c4bd1fac3205e60..590c09ad3873a84ddd795586982dc1e10f35792c 100644
--- a/sky/engine/bindings/core/v8/Nullable.h
+++ b/sky/engine/bindings-dart/common/Nullable.h
@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef SKY_ENGINE_BINDINGS_CORE_V8_NULLABLE_H_
-#define SKY_ENGINE_BINDINGS_CORE_V8_NULLABLE_H_
+#ifndef Nullable_h
+#define Nullable_h
 
-#include "sky/engine/platform/heap/Handle.h"
-#include "sky/engine/wtf/Assertions.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Assertions.h"
 
 namespace blink {
 
@@ -51,6 +51,11 @@ public:
         return (m_isNull && other.m_isNull) || (!m_isNull && !other.m_isNull && m_value == other.m_value);
     }
 
+    void trace(Visitor* visitor)
+    {
+        TraceIfNeeded<T>::trace(visitor, &m_value);
+    }
+
 private:
     T m_value;
     bool m_isNull;
@@ -58,4 +63,4 @@ private:
 
 } // namespace blink
 
-#endif  // SKY_ENGINE_BINDINGS_CORE_V8_NULLABLE_H_
+#endif // Nullable_h