Clean up CodeItemAccessors and Compact/StandardDexFile

Change constructor to use a reference to a dex file.

Remove duplicated logic for GetCodeItemSize.

Bug: 63756964
Test: test-art-host
Change-Id: I69af8b93abdf6bdfa4454e16db8f4e75883bca46
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 07894fd..01155dc 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -911,7 +911,7 @@
   }
   ArenaVector<size_t> covered(
       loop_headers.size(), 0, graph.GetAllocator()->Adapter(kArenaAllocMisc));
-  for (const DexInstructionPcPair& pair : CodeItemInstructionAccessor(&graph.GetDexFile(),
+  for (const DexInstructionPcPair& pair : CodeItemInstructionAccessor(graph.GetDexFile(),
                                                                       &code_item)) {
     const uint32_t dex_pc = pair.DexPc();
     const Instruction& instruction = pair.Inst();