[compiler] Introduce code stubs for string relational comparisons.

src/compiler/simplified-lowering.h

Index: src/compiler/simplified-lowering.h
diff --git a/src/compiler/simplified-lowering.h b/src/compiler/simplified-lowering.h
index 0e66835c1d7bb7a3a6419c40e4bceadbdba8907c..ff93a0df9abcac93164a625d4aa082aa05833014 100644
--- a/src/compiler/simplified-lowering.h
+++ b/src/compiler/simplified-lowering.h
@@ -37,8 +37,6 @@ class SimplifiedLowering final {
                     RepresentationChanger* changer);
   void DoStoreBuffer(Node* node);
   void DoShift(Node* node, Operator const* op, Type* rhs_type);
-  void DoStringLessThan(Node* node);
-  void DoStringLessThanOrEqual(Node* node);
 
   // TODO(bmeurer): This is a gigantic hack to support the gigantic LoadBuffer
   // typing hack to support the gigantic "asm.js should be fast without proper
@@ -57,7 +55,6 @@ class SimplifiedLowering final {
   // position information via the SourcePositionWrapper like all other reducers.
   SourcePositionTable* source_positions_;
 
-  Node* StringComparison(Node* node);
   Node* Int32Div(Node* const node);
   Node* Int32Mod(Node* const node);
   Node* Uint32Div(Node* const node);