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/mirror/field.cc b/runtime/mirror/field.cc
new file mode 100644
index 0000000..1724682
--- /dev/null
+++ b/runtime/mirror/field.cc
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "field-inl.h"
+
+#include "dex_cache-inl.h"
+#include "object_array-inl.h"
+#include "object-inl.h"
+
+namespace art {
+namespace mirror {
+
+GcRoot<Class> Field::static_class_;
+GcRoot<Class> Field::array_class_;
+
+void Field::SetClass(Class* klass) {
+  CHECK(static_class_.IsNull()) << static_class_.Read() << " " << klass;
+  CHECK(klass != nullptr);
+  static_class_ = GcRoot<Class>(klass);
+}
+
+void Field::ResetClass() {
+  CHECK(!static_class_.IsNull());
+  static_class_ = GcRoot<Class>(nullptr);
+}
+
+void Field::SetArrayClass(Class* klass) {
+  CHECK(array_class_.IsNull()) << array_class_.Read() << " " << klass;
+  CHECK(klass != nullptr);
+  array_class_ = GcRoot<Class>(klass);
+}
+
+void Field::ResetArrayClass() {
+  CHECK(!array_class_.IsNull());
+  array_class_ = GcRoot<Class>(nullptr);
+}
+
+void Field::VisitRoots(RootCallback* callback, void* arg) {
+  static_class_.VisitRootIfNonNull(callback, arg, RootInfo(kRootStickyClass));
+  array_class_.VisitRootIfNonNull(callback, arg, RootInfo(kRootStickyClass));
+}
+
+ArtField* Field::GetArtField() {
+  mirror::DexCache* const dex_cache = GetDeclaringClass()->GetDexCache();
+  mirror::ArtField* const art_field = dex_cache->GetResolvedField(GetDexFieldIndex());
+  CHECK(art_field != nullptr);
+  return art_field;
+}
+
+}  // namespace mirror
+}  // namespace art