Move inspector/InspectorValues to platform/JSONValues

This is a pending task that abarth@ mentioned in
http://trac.webkit.org/changeset/116275.
Worked on this because I need the classes to generate JSON for a
window.internals API.

Classes in InspectorValues.h have already been used outside of inspector
to generate JSON strings (http://trac.webkit.org/changeset/116268).
They'll be convenient to use from other parts of blink after moved
to platform/.

BUG=none
TEST=No new tests, no functional change.

Review URL: https://chromiumcodereview.appspot.com/17118009

git-svn-id: svn://svn.chromium.org/blink/trunk@152917 bbb929c8-8fbe-4397-9dbb-9b2b20218538