Revert "Return start/end profiling time in microseconds instead of milliseconds"

This reverts r16049 for breaking build on windows.

TBR=svenpanne@chromium.org,machenbach@chromium.org

Review URL: https://codereview.chromium.org/22189002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16050 ce2b1a6d-e550-0410-aec6-3dcde31c8c00