Fix top-down resolve re-walking graph too much.

Firing off multiple concurrent walks of the same sub-tree with the same
conditions. Data race meant every walk would proceed. Move the logic to
entry of walk function and compare under lock.

Bug: 255526010

Test: m droid

Test: m out/soong/.intermediates/packages/modules/StatsD/apex/com.android.os.statsd/android_common_com.android.os.statsd_image/NOTICE.html.gz

Change-Id: Ie30edbb2ac9eaa9aa55badfc518d51eaadbb6be6