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/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 7a82063..a9cb1cc 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -697,7 +697,8 @@
       CodeGenerator::Create(graph,
                             instruction_set,
                             *compiler_driver->GetInstructionSetFeatures(),
-                            compiler_driver->GetCompilerOptions()));
+                            compiler_driver->GetCompilerOptions(),
+                            compilation_stats_.get()));
   if (codegen.get() == nullptr) {
     MaybeRecordStat(MethodCompilationStat::kNotCompiledNoCodegen);
     return nullptr;