VM: Small clean up and const-ness fix for Thread/OSThread constants.

runtime/bin/thread_android.cc

Index: runtime/bin/thread_android.cc
diff --git a/runtime/bin/thread_android.cc b/runtime/bin/thread_android.cc
index e067e80dbbd48f49c3a4ac7b785665dbf2bc163c..f84a988b4a33e1763e41815b0c3ec914f0a5094d 100644
--- a/runtime/bin/thread_android.cc
+++ b/runtime/bin/thread_android.cc
@@ -114,8 +114,9 @@ int Thread::Start(ThreadStartFunction function, uword parameter) {
 }
 
 
-ThreadLocalKey Thread::kUnsetThreadLocalKey = static_cast<pthread_key_t>(-1);
-ThreadId Thread::kInvalidThreadId = static_cast<ThreadId>(0);
+const ThreadLocalKey Thread::kUnsetThreadLocalKey =
+    static_cast<pthread_key_t>(-1);
+const ThreadId Thread::kInvalidThreadId = static_cast<ThreadId>(0);
 
 ThreadLocalKey Thread::CreateThreadLocal() {
   pthread_key_t key = kUnsetThreadLocalKey;