Rename OatCompilationUnit to Dex.. move to compiler.

Some other clean-up to make fields const and private.

Change-Id: Icad66e2969385ab1f4125162bcbf8d5fa92d3ed5
diff --git a/src/compiler/dex/quick/codegen_util.cc b/src/compiler/dex/quick/codegen_util.cc
index a7ca77a..5f8f6ef 100644
--- a/src/compiler/dex/quick/codegen_util.cc
+++ b/src/compiler/dex/quick/codegen_util.cc
@@ -54,7 +54,7 @@
 bool FastInstance(CompilationUnit* cu,  uint32_t field_idx,
                   int& field_offset, bool& is_volatile, bool is_put)
 {
-  OatCompilationUnit m_unit(cu->class_loader, cu->class_linker,
+  DexCompilationUnit m_unit(cu->class_loader, cu->class_linker,
                             *cu->dex_file, cu->code_item,
                             cu->class_def_idx, cu->method_idx,
                             cu->access_flags);