Let test driver export json results.

BUG=374134
LOG=n
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/285193009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21358 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Comment out %RunMicrotasks assert that triggers in mjsunit tests

TBR=dcarney@chromium.org

Review URL: https://codereview.chromium.org/290313004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21359 ce2b1a6d-e550-0410-aec6-3dcde31c8c00