Stores passed in options in array serializers

This is supported in single serializers. This adds support for passing
options from array serializers to each serializer in it.

lib/active_model/serializer/array_serializer.rb

@@ -7,12 +7,14 @@ module ActiveModel
       attr_reader :meta, :meta_key
 
       def initialize(objects, options = {})
+        options.merge!(root: nil)
+
         @objects = objects.map do |object|
           serializer_class = options.fetch(
             :serializer,
             ActiveModel::Serializer.serializer_for(object)
           )
-          serializer_class.new(object)
+          serializer_class.new(object, options)
         end
         @meta     = options[:meta]
         @meta_key = options[:meta_key]

test/array_serializer_test.rb

@@ -6,7 +6,7 @@ module ActiveModel
       def setup
         @comment = Comment.new
         @post = Post.new
-        @serializer = ArraySerializer.new([@comment, @post])
+        @serializer = ArraySerializer.new([@comment, @post], {some: :options})
       end
 
       def test_respond_to_each
@@ -21,6 +21,8 @@ module ActiveModel
 
         assert_kind_of PostSerializer, serializers.last
         assert_kind_of Post, serializers.last.object
+
+        assert_equal serializers.last.custom_options[:some], :options
       end
     end
   end

test/fixtures/poro.rb

@@ -78,6 +78,10 @@ PostSerializer = Class.new(ActiveModel::Serializer) do
   def blog
     Blog.new(id: 999, name: "Custom blog")
   end
+
+  def custom_options
+    options
+  end
 end
 
 SpammyPostSerializer = Class.new(ActiveModel::Serializer) do