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/thread_state.h b/runtime/thread_state.h
index 6e5deeb..b5479ed 100644
--- a/runtime/thread_state.h
+++ b/runtime/thread_state.h
@@ -41,6 +41,7 @@
   kWaitingInMainSignalCatcherLoop,  // WAITING        TS_WAIT      blocking/reading/processing signals
   kWaitingForDeoptimization,        // WAITING        TS_WAIT      waiting for deoptimization suspend all
   kWaitingForMethodTracingStart,    // WAITING        TS_WAIT      waiting for method tracing to start
+  kWaitingForVisitObjects,          // WAITING        TS_WAIT      waiting for visiting objects
   kStarting,                        // NEW            TS_WAIT      native thread started, not yet ready to run managed code
   kNative,                          // RUNNABLE       TS_RUNNING   running in a JNI native method
   kSuspended,                       // RUNNABLE       TS_RUNNING   suspended by GC or debugger