Fix flaky test ActivityManagerProcessStateTest#testCycleFgsTriangleBiDi

Use new flag to track reachable process during updateOomAdj.

Bug: 144364235
Test: atest MockingOomAdjusterTests
Test: atest CtsAppTestCases:ActivityManagerProcessStateTest
Change-Id: I0605b946a925e4867d31da18e9b90c42cbd8ebb4
diff --git a/services/core/java/com/android/server/am/ProcessRecord.java b/services/core/java/com/android/server/am/ProcessRecord.java
index 1e0693f..5db6ff7 100644
--- a/services/core/java/com/android/server/am/ProcessRecord.java
+++ b/services/core/java/com/android/server/am/ProcessRecord.java
@@ -327,6 +327,8 @@
     int mCachedProcState = ActivityManager.PROCESS_STATE_CACHED_EMPTY;
     int mCachedSchedGroup = ProcessList.SCHED_GROUP_BACKGROUND;
 
+    boolean mReachable; // Whether or not this process is reachable from given process
+
     void setStartParams(int startUid, HostingRecord hostingRecord, String seInfo,
             long startTime) {
         this.startUid = startUid;