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/jni_internal.cc b/runtime/jni_internal.cc
index fd9c40b..e6a35d0 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -37,6 +37,7 @@
 #include "mirror/class_loader.h"
 #include "mirror/object-inl.h"
 #include "mirror/object_array-inl.h"
+#include "mirror/string-inl.h"
 #include "mirror/throwable.h"
 #include "object_utils.h"
 #include "parsed_options.h"