Clean up NullCheck generation and record stats about it.

This removes redundant code from the generators and allows for easier
stat recording.

Change-Id: Iccd4368f9e9d87a6fecb863dee4e2145c97851c4
diff --git a/compiler/optimizing/code_generator_mips64.h b/compiler/optimizing/code_generator_mips64.h
index ba9eaff..9464a14 100644
--- a/compiler/optimizing/code_generator_mips64.h
+++ b/compiler/optimizing/code_generator_mips64.h
@@ -228,8 +228,6 @@
                       const FieldInfo& field_info,
                       bool value_can_be_null);
   void HandleFieldGet(HInstruction* instruction, const FieldInfo& field_info);
-  void GenerateImplicitNullCheck(HNullCheck* instruction);
-  void GenerateExplicitNullCheck(HNullCheck* instruction);
   void GenerateTestAndBranch(HInstruction* instruction,
                              size_t condition_input_index,
                              Mips64Label* true_target,
@@ -354,6 +352,8 @@
   }
 
   void GenerateNop();
+  void GenerateImplicitNullCheck(HNullCheck* instruction);
+  void GenerateExplicitNullCheck(HNullCheck* instruction);
 
  private:
   // Labels for each block that will be compiled.