Add AccessibleObject and Field to mirror

Main motivation is to remove all the functionality / field access on
java side to ArtField. Also comes with some reflection speedups /
slowdowns.

Summary results:
getDeclaredField/getField are slower mostly due to JNI overhead.
However, there is a large speedup in getInt, setInt,
GetInstanceField, and GetStaticField.

Before timings (N5 --compiler-filter=everything):

                       benchmark      ns linear runtime
          Class_getDeclaredField  782.86 ===
                  Class_getField  832.77 ===
                    Field_getInt  160.17 =
                    Field_setInt  195.88 =
                GetInstanceField 3214.38 ==============
                  GetStaticField 6809.49 ==============================

After:
          Class_getDeclaredField 1068.15 ============
                  Class_getField 1180.00 ==============
                    Field_getInt  121.85 =
                    Field_setInt  139.98 =
                GetInstanceField 1986.15 =======================
                  GetStaticField 2523.63 ==============================

Bug: 19264997

Change-Id: Ic0d0fc1b56b95cd6d60f8e76f19caeaa23045c77
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index c462153..d7dd6d0 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -75,6 +75,7 @@
 #include "mirror/art_method-inl.h"
 #include "mirror/class-inl.h"
 #include "mirror/class_loader.h"
+#include "mirror/field.h"
 #include "mirror/stack_trace_element.h"
 #include "mirror/throwable.h"
 #include "monitor.h"
@@ -1291,6 +1292,7 @@
   mirror::StackTraceElement::VisitRoots(callback, arg);
   mirror::String::VisitRoots(callback, arg);
   mirror::Throwable::VisitRoots(callback, arg);
+  mirror::Field::VisitRoots(callback, arg);
   // Visit all the primitive array types classes.
   mirror::PrimitiveArray<uint8_t>::VisitRoots(callback, arg);   // BooleanArray
   mirror::PrimitiveArray<int8_t>::VisitRoots(callback, arg);    // ByteArray