[cashew] stop building our own json/values

These were ripped off from libbase and had int64 support added, but we don't
really need 64 bits of precision; use doubles instead.

BUG=None
TEST=unit

Change-Id: Ia9a3f9bf29e8657dcab1e23203e08516e56d85ea
Signed-off-by: Elly Jones <ellyjones@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/14817
10 files changed