Add perfetto persistent tracing

If a property is set (by shell or by a device build file), perfetto will
keep a simple tracing configuration active all the time.

One test needs to be updated because it assumed that no session with
bugreport_score was running on device. If the property is enabled, that
might not be the case anymore.

Bug: 325622427
Change-Id: I7663f121b44c67ea8d8e23a88c6fb1b588100bfa
diff --git a/tools/gen_android_bp b/tools/gen_android_bp
index 25157e0..561657d 100755
--- a/tools/gen_android_bp
+++ b/tools/gen_android_bp
@@ -282,6 +282,7 @@
         ('min_sdk_version', 'S'),
     ],
     'libperfetto': [('export_include_dirs', {'include', buildflags_dir}),],
+    'perfetto': [('required', {'perfetto_persistent_cfg.pbtxt'}),],
 }