Reduce header files including header files.

Main focus is getting heap.h out of runtime.h.

Change-Id: I8d13dce8512816db2820a27b24f5866cc871a04b
diff --git a/runtime/instrumentation.h b/runtime/instrumentation.h
index 5630862..2dd2cd7 100644
--- a/runtime/instrumentation.h
+++ b/runtime/instrumentation.h
@@ -17,15 +17,15 @@
 #ifndef ART_RUNTIME_INSTRUMENTATION_H_
 #define ART_RUNTIME_INSTRUMENTATION_H_
 
+#include <stdint.h>
+#include <set>
+#include <list>
+
 #include "atomic.h"
 #include "base/macros.h"
 #include "base/mutex.h"
 #include "object_callbacks.h"
 
-#include <stdint.h>
-#include <set>
-#include <list>
-
 namespace art {
 namespace mirror {
   class ArtField;