Add ByteArray interface and provide internal and external implementations.

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 67c3af41e4c370476a9b3e1d84141e58f3421dc9..18544d013768c81275c73dd6153700a743237aa5 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -1094,6 +1094,15 @@ DART_EXPORT Dart_Handle Dart_ListSetAsBytes(Dart_Handle list,
                                             uint8_t* native_array,
                                             intptr_t length);
 
+// --- Byte Arrays ---
+
+DART_EXPORT Dart_Handle Dart_NewByteArray(intptr_t length);
+
+/**
+ * Is this object a ByteArray?
+ */
+DART_EXPORT bool Dart_IsByteArray(Dart_Handle object);
+
 // --- Closures ---
 
 /**