Clean up some includes.

Remove some unnecessary includes from header files, replace
others with forward references and add includes to source
files as needed. Reduce dependency on stack.h by pulling
StackReference<> out to its own file.

Test: m test-art-host
Change-Id: I0fb182145e328870cbd918b0ef6ae2950223c1b2
diff --git a/runtime/reflection.cc b/runtime/reflection.cc
index 44e9bf5..f2af3da 100644
--- a/runtime/reflection.cc
+++ b/runtime/reflection.cc
@@ -29,7 +29,7 @@
 #include "mirror/object_array-inl.h"
 #include "nth_caller_visitor.h"
 #include "scoped_thread_state_change.h"
-#include "stack.h"
+#include "stack_reference.h"
 #include "well_known_classes.h"
 
 namespace art {