Streamline fragment_for SafeBuffer logic to make it more concise and …

…robust against unsafe buffers.

actionpack/lib/action_view/helpers/cache_helper.rb

@@ -51,12 +51,10 @@ def fragment_for(name = {}, options = nil, &block) #:nodoc:
           # This dance is needed because Builder can't use capture
           pos = output_buffer.length
           yield
-          if output_buffer.is_a?(ActionView::OutputBuffer)
-            safe_output_buffer = output_buffer.to_str
-            fragment = safe_output_buffer.slice!(pos..-1)
-            self.output_buffer = ActionView::OutputBuffer.new(safe_output_buffer)
-          else
-            fragment = output_buffer.slice!(pos..-1)
+          output_safe = output_buffer.html_safe?
+          fragment = output_buffer.slice!(pos..-1)
+          if output_safe
+            self.output_buffer = output_buffer.html_safe
           end
           controller.write_fragment(name, fragment, options)
         end