ART: Move JNI files to runtime/jni/ .

Test: Rely on TreeHugger.
Change-Id: I9cae11191ef1567ae9453be498882a7767285140
diff --git a/runtime/thread-inl.h b/runtime/thread-inl.h
index e34f32e..91c27af 100644
--- a/runtime/thread-inl.h
+++ b/runtime/thread-inl.h
@@ -23,7 +23,7 @@
 #include "base/casts.h"
 #include "base/mutex-inl.h"
 #include "base/time_utils.h"
-#include "jni_env_ext.h"
+#include "jni/jni_env_ext.h"
 #include "managed_stack-inl.h"
 #include "obj_ptr.h"
 #include "thread-current-inl.h"