Cache converted markdown (#7159)

Merge pull request 7159

lib/jekyll/converters/markdown.rb

@@ -22,6 +22,8 @@ module Jekyll
           raise Errors::FatalException, "Bailing out; invalid Markdown processor."
         end
 
+        @cache = Jekyll::Cache.new("Jekyll::Converters::Markdown")
+
         @setup = true
       end
 
@@ -89,7 +91,9 @@ module Jekyll
       # Returns a String of the converted content.
       def convert(content)
         setup
-        @parser.convert(content)
+        @cache.getset(content) do
+          @parser.convert(content)
+        end
       end
 
       private

test/test_kramdown.rb

@@ -32,6 +32,7 @@ class TestKramdown < JekyllUnitTest
       @config = Jekyll.configuration(@config)
       @markdown = Converters::Markdown.new(@config)
       @markdown.setup
+      Jekyll::Cache.clear
     end
 
     should "fill symbolized keys into config for compatibility with kramdown" do
@@ -94,7 +95,7 @@ class TestKramdown < JekyllUnitTest
       MARKDOWN
       div_highlight = ">div.highlight"
       selector = "div.highlighter-rouge#{div_highlight}>pre.highlight>code"
-      refute result.css(selector).empty?
+      refute(result.css(selector).empty?, result.to_html)
     end
 
     context "when a custom highlighter is chosen" do