Fold up the SVGLengthContext::convertValueFrom* helpers

Fold up the SVGLengthContext::convertValueFrom* helpers

There are three with similar-looking names, and they are all a single
line each. Fold up where it improves readability, and make the last one
static.
Having folded up convertValueFromUserUnitsToPercentage() we get an
expression that looks like: value * 100 / dimension... * 100; where the
factors (100) obviously cancel out one another. Looking at the single
call-site (SVGLength::setValue) which can actual pass a percentage, it
does an explicit adjustment too. Move that adjustment into the
SVGLengthContext method and drop the two '* 100' - yielding a more
obvious conversion (and less operations to execute).

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=190078

[fs, 2015-02-12 17:48:19]

fs@opera.com changed reviewers:
+ fmalita@chromium.org, pdr@chromium.org

[pdr., 2015-02-12 20:59:16]

The CQ bit was checked by pdr@chromium.org

[pdr., 2015-02-12 20:59:17]

lgtm

[commit-bot: I haz the power, 2015-02-12 20:59:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/897313004/1

[commit-bot: I haz the power, 2015-02-12 21:03:26]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=190078