[jitzygote] Don't spawn a thread in child zygotes.

This prevents forking the zygote until the thread dies. Instead,
check whether the main zygote has finished compiling post-fork
(assuming this happens reasonably soon after compilation is done).

Test: boots with jitzygote config, fork a webview process (settings -> about > license)
Bug: 145973776
Change-Id: Ia854e894cf5c951696d2c4f042607e0edc9ea6c4
1 file changed