RFR: JDK-8188578: move printFramesDocument from HtmlDocWriter to FrameOutputWriter

[Jonathan Gibbons]

Please review a very simple cleanup fix to move an out-of-place method
from HtmlDocWriter to nearer its callsites in FrameOutputWriter.

Cleanup: no new tests required.

JBS: https://bugs.openjdk.java.net/browse/JDK-8188578
Webrev: http://cr.openjdk.java.net/~jjg/8188578/webrev.00/index.html

-- Jon