Include rich_text in diff cache keys

Previously, this wasn't needed: text was normally set to the highlighted
contents anyway. Now, it is: we store different things in text and rich_text.

This caused https://gitlab.com/gitlab-com/production/issues/439.

lib/gitlab/diff/line.rb

 module Gitlab
   module Diff
     class Line
-      SERIALIZE_KEYS = %i(line_code text type index old_pos new_pos).freeze
+      SERIALIZE_KEYS = %i(line_code rich_text text type index old_pos new_pos).freeze
 
       attr_reader :line_code, :type, :index, :old_pos, :new_pos
       attr_writer :rich_text
       attr_accessor :text
 
-      def initialize(text, type, index, old_pos, new_pos, parent_file: nil, line_code: nil)
+      def initialize(text, type, index, old_pos, new_pos, parent_file: nil, line_code: nil, rich_text: nil)
         @text, @type, @index = text, type, index
         @old_pos, @new_pos = old_pos, new_pos
         @parent_file = parent_file
+        @rich_text = rich_text
 
         # When line code is not provided from cache store we build it
         # using the parent_file(Diff::File or Conflict::File).
@@ -18,7 +19,7 @@ module Gitlab
       end
 
       def self.init_from_hash(hash)
-        new(hash[:text], hash[:type], hash[:index], hash[:old_pos], hash[:new_pos], line_code: hash[:line_code])
+        new(hash[:text], hash[:type], hash[:index], hash[:old_pos], hash[:new_pos], line_code: hash[:line_code], rich_text: hash[:rich_text])
       end
 
       def to_hash

spec/lib/gitlab/conflict/file_spec.rb

@@ -69,10 +69,6 @@ describe Gitlab::Conflict::File do
       CGI.unescapeHTML(ActionView::Base.full_sanitizer.sanitize(html)).delete("\n")
     end
 
-    it 'modifies the existing lines' do
-      expect { conflict_file.highlight_lines! }.to change { conflict_file.lines.map(&:instance_variables) }
-    end
-
     it 'is called implicitly when rich_text is accessed on a line' do
       expect(conflict_file).to receive(:highlight_lines!).once.and_call_original
 

spec/lib/gitlab/diff/line_spec.rb

 describe Gitlab::Diff::Line do
+  describe '.init_from_hash' do
+    it 'round-trips correctly with to_hash' do
+      line = described_class.new('<input>', 'match', 0, 0, 1,
+                                 parent_file: double(:file),
+                                 line_code: double(:line_code),
+                                 rich_text: '&lt;input&gt;')
+
+      expect(described_class.init_from_hash(line.to_hash).to_hash)
+        .to eq(line.to_hash)
+    end
+  end
+
   context "when setting rich text" do
     it 'escapes any HTML special characters in the diff chunk header' do
       subject = described_class.new("<input>", "", 0, 0, 0)