Cache field lowering info in mir_graph.

Change-Id: I9f9d76e3ae6c31e88bdf3f59820d31a625da020f
diff --git a/compiler/dex/mir_graph.cc b/compiler/dex/mir_graph.cc
index 2bfc154..46e854f 100644
--- a/compiler/dex/mir_graph.cc
+++ b/compiler/dex/mir_graph.cc
@@ -87,7 +87,9 @@
       compiler_temps_(arena, 6, kGrowableArrayMisc),
       num_non_special_compiler_temps_(0),
       max_available_non_special_compiler_temps_(0),
-      punt_to_interpreter_(false) {
+      punt_to_interpreter_(false),
+      ifield_lowering_infos_(arena, 0u),
+      sfield_lowering_infos_(arena, 0u) {
   try_block_addr_ = new (arena_) ArenaBitVector(arena_, 0, true /* expandable */);
   max_available_special_compiler_temps_ = std::abs(static_cast<int>(kVRegNonSpecialTempBaseReg))
       - std::abs(static_cast<int>(kVRegTempBaseReg));