Instead of having the "next step" state machine logic in the compiler
dispatcher, move it to the compiler dispatcher job. This is a
prerequisite to having more generic jobs with slightly different state
sets, such as an optimizing compile job.

Bug: v8:6537
Change-Id: Ib7319222f26dbc0e2afc95573b06d813825afde3
Reviewed-on: https://chromium-review.googlesource.com/554751
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46396}