mojom: Add associative arrays to the mojom language.

mojo/public/tools/bindings/generators/cpp_templates/struct_serialization_definition.tmpl

 size_t GetSerializedSize_(const {{struct.name}}Ptr& input) {
   if (!input)
     return 0;
   size_t size = sizeof(internal::{{struct.name}}_Data);
 {%- for pf in struct.packed.packed_fields if pf.field.kind|is_object_kind %}
   size += GetSerializedSize_(input->{{pf.field.name}});
 {%- endfor %}
   return size;
 }
 
 void Serialize_({{struct.name}}Ptr input, mojo::internal::Buffer* buf,
                 internal::{{struct.name}}_Data** output) {
   if (input) {
     internal::{{struct.name}}_Data* result =
         internal::{{struct.name}}_Data::New(buf);
 {%- for pf in struct.packed.packed_fields %}
 {%-   if pf.field.kind|is_object_kind %}
 {%-     if pf.field.kind|is_any_array_kind %}
     mojo::SerializeArray_<{{pf.field.kind|get_array_validate_params|indent(26)}}>(
         mojo::internal::Forward(input->{{pf.field.name}}), buf, &result->{{pf.field.name}}.ptr);
+{%-     elif pf.field.kind|is_map_kind %}
+    mojo::Array<{{pf.field.kind.key_kind|cpp_result_type}}> {{pf.field.name}}_keys;
+    mojo::Array<{{pf.field.kind.value_kind|cpp_result_type}}> {{pf.field.name}}_values;
+    input->{{pf.field.name}}.DecomposeMapTo(&{{pf.field.name}}_keys,
+                                            &{{pf.field.name}}_values);
+
+    mojo::SerializeArray_<{{pf.field.kind.key_kind|get_map_validate_params|indent(26)}}>(
+        mojo::internal::Forward({{pf.field.name}}_keys), buf, &result->{{pf.field.name}}_keys.ptr);
+    mojo::SerializeArray_<{{pf.field.kind.value_kind|get_map_validate_params|indent(26)}}>(
+        mojo::internal::Forward({{pf.field.name}}_values), buf, &result->{{pf.field.name}}_values.ptr);
 {%-     else %}
     Serialize_(mojo::internal::Forward(input->{{pf.field.name}}), buf, &result->{{pf.field.name}}.ptr);
 {%-     endif %}
 {%-     if not pf.field.kind|is_nullable_kind %}
+{%-       if pf.field.kind|is_map_kind %}
+    MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
+        !result->{{pf.field.name}}_keys.ptr,
+        mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
+        "null key array for {{pf.field.name}} field in {{struct.name}} struct");
+    MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
+        !result->{{pf.field.name}}_values.ptr,
+        mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
+        "null value array for {{pf.field.name}} field in {{struct.name}} struct");
+{%-       else %}
     MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
         !result->{{pf.field.name}}.ptr,
         mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
         "null {{pf.field.name}} field in {{struct.name}} struct");
+{%-       endif %}
 {%-     endif %}
 {%-   elif pf.field.kind|is_any_handle_kind %}
 {%-     if pf.field.kind|is_interface_kind %}
     result->{{pf.field.name}} = input->{{pf.field.name}}.PassMessagePipe().release();
 {%-     else %}
     result->{{pf.field.name}} = input->{{pf.field.name}}.release();
 {%-     endif %}
 {%-     if not pf.field.kind|is_nullable_kind %}
     MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
         !result->{{pf.field.name}}.is_valid(),
         mojo::internal::VALIDATION_ERROR_UNEXPECTED_INVALID_HANDLE,
         "invalid {{pf.field.name}} field in {{struct.name}} struct");
 {%-     endif %}
 {%-   else %}
     result->{{pf.field.name}} = input->{{pf.field.name}};
 {%-   endif %}
 {%- endfor %}
     *output = result;
   } else {
     *output = nullptr;
   }
 }
 
 void Deserialize_(internal::{{struct.name}}_Data* input,
                   {{struct.name}}Ptr* output) {
   if (input) {
     {{struct.name}}Ptr result({{struct.name}}::New());
 {%- for pf in struct.packed.packed_fields %}
-{%-   if pf.field.kind|is_object_kind %}
+{%-   if pf.field.kind|is_map_kind %}
+    mojo::Array<{{pf.field.kind.key_kind|cpp_result_type}}> {{pf.field.name}}_keys;
+    Deserialize_(input->{{pf.field.name}}_keys.ptr, &{{pf.field.name}}_keys);
+    mojo::Array<{{pf.field.kind.value_kind|cpp_result_type}}> {{pf.field.name}}_values;
+    Deserialize_(input->{{pf.field.name}}_values.ptr, &{{pf.field.name}}_values);
+    result->{{pf.field.name}} =
+         mojo::Map<{{pf.field.kind.key_kind|cpp_result_type}},
+                   {{pf.field.kind.value_kind|cpp_result_type}}>(
+             {{pf.field.name}}_keys.Pass(),
+             {{pf.field.name}}_values.Pass()).Pass();
+{%-   elif pf.field.kind|is_object_kind %}
     Deserialize_(input->{{pf.field.name}}.ptr, &result->{{pf.field.name}});
 {%-   elif pf.field.kind|is_interface_kind %}
     if (input->{{pf.field.name}}.is_valid())
       result->{{pf.field.name}}.Bind(mojo::MakeScopedHandle(mojo::internal::FetchAndReset(&input->{{pf.field.name}})));
 {%-   elif pf.field.kind|is_any_handle_kind %}
     result->{{pf.field.name}}.reset(mojo::internal::FetchAndReset(&input->{{pf.field.name}}));
 {%-   elif pf.field.kind|is_enum_kind %}
     result->{{pf.field.name}} = static_cast<{{pf.field.kind|cpp_wrapper_type}}>(
       input->{{pf.field.name}});
 {%-   else %}
     result->{{pf.field.name}} = input->{{pf.field.name}};
 {%-   endif %}
 {%- endfor %}
     *output = result.Pass();
   } else {
     output->reset();
   }
 }