Reduce header files including header files.

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

Change-Id: I8d13dce8512816db2820a27b24f5866cc871a04b
diff --git a/runtime/parsed_options.h b/runtime/parsed_options.h
index a27eec6..d0f3c12 100644
--- a/runtime/parsed_options.h
+++ b/runtime/parsed_options.h
@@ -19,6 +19,7 @@
 
 #include <string>
 
+#include "gc/collector_type.h"
 #include "runtime.h"
 #include "trace.h"