Add multi-line suggestion migrations

Adds outdated, lines_above and lines_below columns to
suggestions table.

outdated - boolean which represents whether the suggestion
is outdated or not. For instance, if any line changed after
you left the multi-line suggestion, even though the note
is not outdated, it helps tracking if the content has changed
in the latest file. We cache this information in a column given
it's not a cheap operation to do for every suggestion in the
request time.
lines_below, lines_above - persists the parsed arguments from
`suggestion:-10+3` syntax, where `10` would be lines_above and
3 lines_below. We need that to dynamically calculate which
lines we should monitor for outdating / persisting the correct
content in from_content column.

db/migrate/20190228192410_add_multi_line_attributes_to_suggestion.rb

+# frozen_string_literal: true
+
+class AddMultiLineAttributesToSuggestion < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default :suggestions, :outdated, :boolean, default: false, allow_null: false
+    add_column_with_default :suggestions, :lines_above, :integer, default: 0, allow_null: false
+    add_column_with_default :suggestions, :lines_below, :integer, default: 0, allow_null: false
+  end
+
+  def down
+    remove_columns :suggestions, :outdated, :lines_above, :lines_below
+  end
+end

db/schema.rb

@@ -2039,6 +2039,9 @@ ActiveRecord::Schema.define(version: 20190322132835) do
     t.string "commit_id"
     t.text "from_content", null: false
     t.text "to_content", null: false
+    t.boolean "outdated", default: false, null: false
+    t.integer "lines_above", default: 0, null: false
+    t.integer "lines_below", default: 0, null: false
     t.index ["note_id", "relative_order"], name: "index_suggestions_on_note_id_and_relative_order", unique: true, using: :btree
   end