Add Handle/HandleScope and delete SirtRef.

Delete SirtRef and replaced it with Handle. Handles are value types
which wrap around StackReference*.

Renamed StackIndirectReferenceTable to HandleScope.

Added a scoped handle wrapper which wraps around an Object** and
restores it in its destructor.

Renamed Handle::get -> Get.

Bug: 8473721

Change-Id: Idbfebd4f35af629f0f43931b7c5184b334822c7a
diff --git a/runtime/mirror/string.h b/runtime/mirror/string.h
index f97308e..169b671 100644
--- a/runtime/mirror/string.h
+++ b/runtime/mirror/string.h
@@ -24,7 +24,7 @@
 
 namespace art {
 
-template<class T> class SirtRef;
+template<class T> class Handle;
 struct StringClassOffsets;
 struct StringOffsets;
 class StringPiece;
@@ -137,7 +137,7 @@
   static String* Alloc(Thread* self, int32_t utf16_length)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
-  static String* Alloc(Thread* self, const SirtRef<CharArray>& array)
+  static String* Alloc(Thread* self, const Handle<CharArray>& array)
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
   void SetArray(CharArray* new_array) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);