[mojo] Allow value deserialization to fail

mojo/public/cpp/bindings/lib/map_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_MAP_SERIALIZATION_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_MAP_SERIALIZATION_H_
 
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 #include "mojo/public/cpp/bindings/lib/map_data_internal.h"
 #include "mojo/public/cpp/bindings/lib/map_internal.h"
@@ skipping 144 matching lines @@
     *output = result;
   } else {
     *output = nullptr;
   }
 }
 
 template <typename MapKey,
           typename MapValue,
           typename DataKey,
           typename DataValue>
-inline void Deserialize_(internal::Map_Data<DataKey, DataValue>* input,
+inline bool Deserialize_(internal::Map_Data<DataKey, DataValue>* input,
                          Map<MapKey, MapValue>* output,
                          internal::SerializationContext* context) {
   if (input) {
     Array<MapKey> keys;
     Array<MapValue> values;
 
-    Deserialize_(input->keys.ptr, &keys, context);
-    Deserialize_(input->values.ptr, &values, context);
+    if (!Deserialize_(input->keys.ptr, &keys, context))
+      return false;
+    if (!Deserialize_(input->values.ptr, &values, context))
+      return false;
 
     *output = Map<MapKey, MapValue>(keys.Pass(), values.Pass());
   } else {
     output->reset();
   }
+  return true;
 }
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MAP_SERIALIZATION_H_