[turbofan] Add comments to CodeAssembler

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 211d17d6312102153ceb04d3756410350a102931..37a84981a2f5927340f9084d05b4f72e719a2f89 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -194,6 +194,7 @@ class MachineOperatorBuilder final : public ZoneObject {
       AlignmentRequirements alignmentRequirements =
           AlignmentRequirements::NoUnalignedAccessSupport());
 
+  const Operator* Comment(const char* msg);
   const Operator* DebugBreak();
 
   const Operator* Word32And();
@@ -628,6 +629,7 @@ class MachineOperatorBuilder final : public ZoneObject {
 #undef PSEUDO_OP_LIST
 
  private:
+  Zone* zone_;
   MachineOperatorGlobalCache const& cache_;
   MachineRepresentation const word_;
   Flags const flags_;