Clean up the locks around Heap::VisitObjects().

This is so that we could support suspending all threads when visiting
objects in the presence of a concurrent, moving collector.

Bug: 12687968
Change-Id: Icc8e60630465afde948ebc6ea91d4ebaff5d7837
diff --git a/runtime/native/java_lang_Thread.cc b/runtime/native/java_lang_Thread.cc
index 760eb9b..e4b8db1 100644
--- a/runtime/native/java_lang_Thread.cc
+++ b/runtime/native/java_lang_Thread.cc
@@ -88,6 +88,7 @@
     case kWaitingForSignalCatcherOutput:  return kJavaWaiting;
     case kWaitingInMainSignalCatcherLoop: return kJavaWaiting;
     case kWaitingForMethodTracingStart:   return kJavaWaiting;
+    case kWaitingForVisitObjects:         return kJavaWaiting;
     case kSuspended:                      return kJavaRunnable;
     // Don't add a 'default' here so the compiler can spot incompatible enum changes.
   }