Move StringPiece into the base namespace. It is colliding

Move StringPiece into the base namespace.  It is colliding
with the StringPiece class in icu4.2, which is a problem
when trying to use the system version of icu.

[tony, 2009-09-10 18:30:01]

I will also roll hunspell deps once http://codereview.chromium.org/193073 lands.

[agl, 2009-09-10 18:31:40]

If the try bots like it: LGTM

[jungshik at Google, 2009-09-10 20:58:20]

On 2009/09/10 18:31:40, agl wrote:
> If the try bots like it: LGTM

same here :-)

Thanks for the CL !