We're refactoring startup tracing in Chrome, see design doc[1]. With
the new startup tracing architecture, each process needs to allocate a
shared memory buffer when enabling startup tracing.
In zygote child processes, this is only possible after mojo's IPC
support is brought up, because the mojo broker has to create the buffer
on the process's behalf (the zygote sandbox prevents the child processes
from doing this themselves).
To prepare for the startup tracing refactor, this patch moves startup
tracing initialization for zygote child processes from
ContentMainRunner to their respective main functions, until after mojo
is brought up by the respective ChildThreadImpl subclass.
We should only lose minimal tracing data due to this change (from the
early part of the respective main function), and only from zygote
children (primarily renderer + utility processes) on Linux/ChromeOS.
[1] https://docs.google.com/document/d/1FygJQbD29vMkfVfT7m0Lb1u1zZZU1VgXAPi_R0uBoTw/edit?usp=sharing
Bug: 1006753
Change-Id: I59c21b2b383c755925dc5ff0c19160985e089800
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2038574
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739869}
39c6f5a6d8