mojo: Fix c++ bindings so serialization of empty arrays doesn't crash.

mojo/public/cpp/bindings/lib/array_serialization.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 MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_H_
 
 #include <string.h>  // For |memcpy()|.
 
 #include <vector>
@@ skipping 45 matching lines @@
   }
   template <bool element_is_nullable, typename ElementValidateParams>
   static void SerializeElements(Array<E> input,
                                 Buffer* buf,
                                 Array_Data<F>* output) {
     static_assert(!element_is_nullable,
                   "Primitive type should be non-nullable");
     static_assert((IsSame<ElementValidateParams, NoValidateParams>::value),
                   "Primitive type should not have array validate params");
 
-    memcpy(output->storage(), &input.storage()[0], input.size() * sizeof(E));
+    if (input.size())
+      memcpy(output->storage(), &input.storage()[0], input.size() * sizeof(E));
   }
   static void DeserializeElements(Array_Data<F>* input, Array<E>* output) {
     std::vector<E> result(input->size());
-    memcpy(&result[0], input->storage(), input->size() * sizeof(E));
+    if (input->size())
+      memcpy(&result[0], input->storage(), input->size() * sizeof(E));
     output->Swap(&result);
   }
 };
 
 template <>
 struct ArraySerializer<bool, bool, false> {
   static size_t GetSerializedSize(const Array<bool>& input) {
     return sizeof(Array_Data<bool>) + Align((input.size() + 7) / 8);
   }
   template <bool element_is_nullable, typename ElementValidateParams>
@@ skipping 209 matching lines @@
   if (input) {
     internal::ArraySerializer<E, F>::DeserializeElements(input, output);
   } else {
     output->reset();
   }
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_SERIALIZATION_H_