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/art_field.cc b/runtime/mirror/art_field.cc
index 7b0b94c..8eb30f9 100644
--- a/runtime/mirror/art_field.cc
+++ b/runtime/mirror/art_field.cc
@@ -60,7 +60,7 @@
     }
   }
   // Not called within a transaction.
-  SetField32<false>(OFFSET_OF_OBJECT_MEMBER(ArtField, offset_), num_bytes.Uint32Value(), false);
+  SetField32<false>(OFFSET_OF_OBJECT_MEMBER(ArtField, offset_), num_bytes.Uint32Value());
 }
 
 void ArtField::VisitRoots(RootCallback* callback, void* arg) {