Add option to force passing alt=json for some APIs that return xml by default

lib/google/apis/generator/annotator.rb

@@ -90,6 +90,10 @@ module Google
           @path.reduce('') { |a, e| a + '/' + e }
         end
 
+        def option(opt_name)
+          @names[sprintf('%s?%s', key, opt_name)]
+        end
+
         private
 
         # For RPC style methods, pick a name based off the request objects.
@@ -184,6 +188,7 @@ module Google
                 value.constant = constantize_scope(key)
               end
             end
+            @rest_description.force_alt_json = @names.option('force_alt_json')
             @rest_description.parameters.reject! { |k, _v| PARAMETER_BLACKLIST.include?(k) }
             annotate_parameters(@rest_description.parameters)
             annotate_resource(@rest_description.name, @rest_description)

lib/google/apis/generator/model.rb

@@ -99,6 +99,9 @@ module Google
       end
 
       class RestDescription
+        attr_accessor :force_alt_json
+        alias_method :force_alt_json?, :force_alt_json
+
         def version
           ActiveSupport::Inflector.camelize(@version.gsub(/\W/, '-')).gsub(/-/, '_')
         end

lib/google/apis/generator/templates/_method.tmpl

@@ -73,6 +73,9 @@ def <%= api_method.generated_name %>(<% for param in api_method.required_paramet
   command.request_object = <%= api.schemas[api_method.request._ref].generated_name %>_object
 <% end -%>
 <% if api_method.response -%>
+<%   if api.force_alt_json? -%>
+  command.query['alt'] = 'json'
+<%   end -%>
   command.response_representation = <%= api.schemas[api_method.response._ref].generated_type %>::Representation
   command.response_class = <%= api.schemas[api_method.response._ref].generated_type %>
 <% end -%>