Moved setting of visual ordering from DocumentWriter to DecodedDataDocument

This means DocumentParser::appendBytes and DocumentParser::flush don't need to return the number of bytes decoded anymore, which is another step on the way to be able to do the decoding on the parser thread, and additionally cleans the code up a bit.

Builds on https://codereview.chromium.org/69823002/

BUG=277886

Review URL: https://codereview.chromium.org/73293003

git-svn-id: svn://svn.chromium.org/blink/trunk@162262 bbb929c8-8fbe-4397-9dbb-9b2b20218538