Use rounding when converting desiredScale to a sampleSize

Use rounding when converting desiredScale to a sampleSize

Right now we have a bug in Gold where some images are labeled
_0.167 and others are labeled _0.166.  They are all 1/6
scales and should be labeled the same way and compared.

The fix involves changing 0.166 to 0.167 in the list of
scales that we test on, but SkScaledCodec does not scale
to 0.167 as I expected.

SkScaledCodec converts 0.167 to sampleSize = 5.999 and then
casts to sampleSize = 5.  I would argue that we should do
a true round, so 0.167 represents a sampleSize of 6.

In general, this CL change onGetScaledDimensions so that
we now round desiredScale to the nearest sampleSize.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/6c50a8f4ab0747b319914c4b600a2e74c6d6e721

[msarett, 2015-09-18 15:26:20]

msarett@google.com changed reviewers:
+ scroggo@google.com

[scroggo, 2015-09-18 15:57:26]

lgtm

[msarett, 2015-09-18 18:17:08]

The CQ bit was checked by msarett@google.com

[commit-bot: I haz the power, 2015-09-18 18:17:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356923002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356923002/1

[commit-bot: I haz the power, 2015-09-18 18:24:47]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/6c50a8f4ab0747b319914c4b600a2e74c6d6e721