Remove SkRecorder's kWriteOnly mode.

Remove SkRecorder's kWriteOnly mode.

I'm soon going to have SkRecorder start calling getTotalMatrix(), which
would be broken in write-only mode.  That change is big and nebulous,
but it's clear kWriteOnly needs to go, so we might as well kill it now.

My notes in bench_playback about kWriteOnly mode being important were
probably overly cautious.  I now think this is a fair enough comparison
even re-recording into a read-write canvas.

BUG=skia:2378
Committed: http://code.google.com/p/skia/source/detail?r=14963

[mtklein, 2014-05-29 16:00:06]

lgtm

[commit-bot: I haz the power, 2014-05-29 16:00:53]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/290653004/20001

[commit-bot: I haz the power, 2014-05-29 16:52:46]

Change committed as 14963