Fix for partial filter subregion specification with deferred filters.

Fix for partial filter subregion specification with deferred filters.

Filter primitive subregions are specified as x/y/width/height, while
skia crop rects are left/right/top/bottom.  If x is set but
width is not, we were only sending the left edge. We must also tell skia
the right edge, in order to preserve the rect's original width.
Similarly when y is specified but height is not, we must tell skia the
new bottom edge.

Also changed all this code to use FloatRect instead of SkRect, since
these relationships are easier to express.

Covered by layout test svg/batik/filters/filterRegions.svg, when run
with --enable-deferred-filters.

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170116

[Stephen White, 2014-03-26 23:38:40]

Florin: PTAL. Thanks!

[f(malita), 2014-03-27 00:57:36]

lgtm

[Stephen White, 2014-03-27 01:00:48]

The CQ bit was checked by senorblanco@chromium.org

[commit-bot: I haz the power, 2014-03-27 01:00:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/senorblanco@chromium.org/212803005/1

[commit-bot: I haz the power, 2014-03-27 01:11:27]

Change committed as 170116