Make CodeItem fields private

Make code item fields private and use accessors. Added a hand full of
friend classes to reduce the size of the change.

Changed default to be nullable and removed CreateNullable.
CreateNullable was a bad API since it defaulted to the unsafe, may
add a CreateNonNullable if it's important for performance.

Motivation:
Have a different layout for code items in cdex.

Bug: 63756964
Test: test-art-host-gtest
Test: test/testrunner/testrunner.py --host
Test: art/tools/run-jdwp-tests.sh '--mode=host' '--variant=X32' --debug

Change-Id: I42bc7435e20358682075cb6de52713b595f95bf9
diff --git a/compiler/compiler.cc b/compiler/compiler.cc
index bb614ae..47f44ff 100644
--- a/compiler/compiler.cc
+++ b/compiler/compiler.cc
@@ -19,6 +19,7 @@
 #include <android-base/logging.h>
 
 #include "base/macros.h"
+#include "code_item_accessors-inl.h"
 #include "driver/compiler_driver.h"
 #include "optimizing/optimizing_compiler.h"
 #include "utils.h"
@@ -46,15 +47,16 @@
    * Dalvik uses 16-bit uints for instruction and register counts.  We'll limit to a quarter
    * of that, which also guarantees we cannot overflow our 16-bit internal Quick SSA name space.
    */
-  if (code_item.insns_size_in_code_units_ >= UINT16_MAX / 4) {
+  CodeItemDataAccessor accessor(&dex_file, &code_item);
+  if (accessor.InsnsSizeInCodeUnits() >= UINT16_MAX / 4) {
     LOG(INFO) << "Method exceeds compiler instruction limit: "
-              << code_item.insns_size_in_code_units_
+              << accessor.InsnsSizeInCodeUnits()
               << " in " << dex_file.PrettyMethod(method_idx);
     return true;
   }
-  if (code_item.registers_size_ >= UINT16_MAX / 4) {
+  if (accessor.RegistersSize() >= UINT16_MAX / 4) {
     LOG(INFO) << "Method exceeds compiler virtual register limit: "
-              << code_item.registers_size_ << " in " << dex_file.PrettyMethod(method_idx);
+              << accessor.RegistersSize() << " in " << dex_file.PrettyMethod(method_idx);
     return true;
   }
   return false;