Ensure that conversions from/to 8bit and 16bit never return null string.

Ensure that conversions from/to 8bit and 16bit never return null string.

WTF::StringImpl::upconvertedString() relies on make16BitFrom8BitSource()
return a valid (non-null) string, on which releaseImpl() can be called.
The patch ensures that for zero length sources an empty string is
returned. The same logic is applied to make8BitFrom16BitSource().

R=abarth@chromium.org
BUG=409977
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181263

[abarth-chromium, 2014-09-02 21:44:36]

The CQ bit was checked by abarth@chromium.org

[abarth-chromium, 2014-09-02 21:44:36]

lgtm

[commit-bot: I haz the power, 2014-09-02 21:45:41]

CQ is trying da patch. Follow status at

https://chromium-status.appspot.com/cq/rhodovan.u-szeged@partner.samsung.com/...

[commit-bot: I haz the power, 2014-09-02 22:52:25]

Committed patchset #1 (id:1) as 181263