Force inlining on trivial accessors.

Make volatility for GetFieldObject a template parameter.
Move some trivial mirror::String routines to a -inl.h.

Bug: 14285442

Change-Id: Ie23b11d4f18cb15a62c3bbb42837a8aaf6b68f92
diff --git a/runtime/mirror/iftable.h b/runtime/mirror/iftable.h
index bb4cd41..ad312ed 100644
--- a/runtime/mirror/iftable.h
+++ b/runtime/mirror/iftable.h
@@ -17,6 +17,7 @@
 #ifndef ART_RUNTIME_MIRROR_IFTABLE_H_
 #define ART_RUNTIME_MIRROR_IFTABLE_H_
 
+#include "base/casts.h"
 #include "object_array.h"
 
 namespace art {