Add sensitive netlog tracing to Cronet

This CL makes it possible to gather unredacted netlogs in a Cronet
Perfetto trace. Previously, this could only be done with "heavily
redacted" netlogs.

Unredacted netlogs are highly privacy and security sensitive. For this
reason, Cronet will only trace unredacted netlogs if the user jumps
through a number of hoops:

 - They must be using a debug Android OS build, OR the app using Cronet
   must be marked as "debuggable" in its manifest;

 - They must explicitly enable the feature on their device using the
   `debug.cronet.trace_netlog` system property (adb shell setprop);

 - When the feature is enabled netlogs are sent to a different trace
   category that is disabled by default, which means the Perfetto trace
   config must be explicitly set up to capture unredacted netlogs.

Bug: 410018349
Change-Id: Ibbfd71b6638f8db93ca107b8fef3be74ee035818
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6523443
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Stefano Duo <stefanoduo@google.com>
Reviewed-by: Antonio Sartori <antoniosartori@chromium.org>
Auto-Submit: Etienne Dechamps <edechamps@google.com>
Commit-Queue: Antonio Sartori <antoniosartori@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1461180}