[turbofan] Add support for copy-on-write element stores.

src/compiler/typer.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/typer.h"
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph-reducer.h"
@@ skipping 701 matching lines @@
   return nullptr;
 }
 
 Type* Typer::Visitor::TypeLoopExitValue(Node* node) { return Operand(node, 0); }
 
 Type* Typer::Visitor::TypeLoopExitEffect(Node* node) {
   UNREACHABLE();
   return nullptr;
 }
 
+Type* Typer::Visitor::TypeEnsureWritableFastElements(Node* node) {
+  return Operand(node, 1);
+}
+
 Type* Typer::Visitor::TypeTransitionElementsKind(Node* node) {
   UNREACHABLE();
   return nullptr;
 }
 
 Type* Typer::Visitor::TypeCheckpoint(Node* node) {
   UNREACHABLE();
   return nullptr;
 }
 
@@ skipping 1560 matching lines @@
   }
   if (Type::IsInteger(*value)) {
     return Type::Range(value->Number(), value->Number(), zone());
   }
   return Type::Constant(value, zone());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8