[GWP-ASan] Maybe initialise GWP-ASan from Zygote.

Calls the GWP-ASan mallopt() to possibly install GWP-ASan for the zygote
child.

Bug: 135634846
Test: ??
Change-Id: I08d6797fa9b5ca10b97e0ab1efc2dc1c219c1b45

core/jni/com_android_internal_os_Zygote.cpp

@@ -579,6 +579,12 @@ static void PreApplicationInit() {
 
   // Set the jemalloc decay time to 1.
   mallopt(M_DECAY_TIME, 1);
+
+  // Maybe initialize GWP-ASan here. Must be called after
+  // mallopt(M_SET_ZYGOTE_CHILD).
+  bool ForceEnableGwpAsan = false;
+  android_mallopt(M_INITIALIZE_GWP_ASAN, &ForceEnableGwpAsan,
+                  sizeof(ForceEnableGwpAsan));
 }
 
 static void SetUpSeccompFilter(uid_t uid, bool is_child_zygote) {