ART: Turn off unattached thread dumping

May be responsible for lack of ANR dumps in some situations.

Bug: 29248079
Change-Id: Ib742c063b1d77216eddfbf4392d17d024e028bf8
diff --git a/runtime/thread_list.cc b/runtime/thread_list.cc
index 1e5264c..d11aa3c 100644
--- a/runtime/thread_list.cc
+++ b/runtime/thread_list.cc
@@ -59,7 +59,8 @@
 
 // Whether we should try to dump the native stack of unattached threads. See commit ed8b723 for
 // some history.
-static constexpr bool kDumpUnattachedThreadNativeStack = true;
+// Turned off again. b/29248079
+static constexpr bool kDumpUnattachedThreadNativeStack = false;
 
 ThreadList::ThreadList()
     : suspend_all_count_(0),