Drop assert for degenerate cases in FloatRoundedRect::radiusCenterRect()

Drop assert for degenerate cases in FloatRoundedRect::radiusCenterRect()

This method is only used by BoxClipper, to provide a conservative
estimate of a rectangle enclosed by the rounded (inner) rectangle.
Since it's unproblematic to provide a conservative estimate for the
"degenerate" cases [1], do that instead of asserting.
Reformulate the implementation using FloatRectOutsets. The only
functional change is that there no longer is an implicit conversion
from float to int.

[1] As defined by isRenderable().

BUG=458505, 477826
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=195299

[fs, 2015-05-11 12:59:58]

fs@opera.com changed reviewers:
+ chrishtr@chromium.org, jbroman@chromium.org

[fs, 2015-05-11 12:59:59]

The description briefly mentions the motivation for the removal, but to spell it
out a bit more: BoxClipper works with an inner (padding edge) border - a case
mentioned specifically in the spec:

"Note that if the center of a corner's outer curve is past an opposite padding
edge (in the border area of a side opposite the corner), the inner curve will
not be a full quarter ellipse."

The isRenderable() check however is related to what GC::fillRoundedRect(...)
will accept and be able to handle. Given this it might even make sense to make
radiusCenterRect() local to BoxClipper instead (given it's the only user.)

[chrishtr, 2015-05-13 06:18:10]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2015-05-13 06:18:10]

lgtm

[commit-bot: I haz the power, 2015-05-13 06:18:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1136083002/1

[commit-bot: I haz the power, 2015-05-13 07:30:55]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=195299