Update stale comment for dalvik.vm.stack-trace-file.

Test: make
Change-Id: Ia14494b146f58937aed203271be340747817519b
diff --git a/core/main.mk b/core/main.mk
index a36251d..4ce5e67 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -453,8 +453,8 @@
 
 ADDITIONAL_BUILD_PROPERTIES += net.bt.name=Android
 
-# enable vm tracing in files for now to help track
-# the cause of ANRs in the content process
+# Sets the location that the runtime dumps stack traces to when signalled
+# with SIGQUIT. Stack trace dumping is turned on for all android builds.
 ADDITIONAL_BUILD_PROPERTIES += dalvik.vm.stack-trace-file=/data/anr/traces.txt
 
 # ------------------------------------------------------------