Allow Mojo structs as map keys

mojo/public/cpp/bindings/native_struct.h

 // Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_NATIVE_STRUCT_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_NATIVE_STRUCT_H_
 
 #include "mojo/public/cpp/bindings/array.h"
 #include "mojo/public/cpp/bindings/lib/native_struct_data.h"
 #include "mojo/public/cpp/bindings/struct_ptr.h"
@@ skipping 20 matching lines @@
   template <typename U>
   U To() const {
     return TypeConverter<U, NativeStruct>::Convert(*this);
   }
 
   NativeStruct();
   ~NativeStruct();
 
   NativeStructPtr Clone() const;
   bool Equals(const NativeStruct& other) const;
+  size_t Hash(size_t seed) const;
 
   Array<uint8_t> data;
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_NATIVE_STRUCT_H_