[builtins] Move StringIndexOf to a builtin.

src/builtins/builtins-string.cc

 // Copyright 2016 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/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 
 #include "src/code-factory.h"
 
 namespace v8 {
@@ skipping 459 matching lines @@
     assembler->Return(assembler->NaNConstant());
     assembler->Bind(&if_positioninbounds);
   }
 
   // Load the character at the {position} from the {receiver}.
   Node* value = assembler->StringCharCodeAt(receiver, position);
   Node* result = assembler->SmiFromWord32(value);
   assembler->Return(result);
 }
 
+// ES6 section 21.1.3.8 String.prototype.indexOf ( searchString [ , position ] )
+BUILTIN(StringPrototypeIndexOf) {
+  HandleScope handle_scope(isolate);
+
+  return String::IndexOf(isolate, args.receiver(),
+                         args.atOrUndefined(isolate, 1),
+                         args.atOrUndefined(isolate, 2));
+}
+
 // ES6 section 21.1.3.9
 // String.prototype.lastIndexOf ( searchString [ , position ] )
 BUILTIN(StringPrototypeLastIndexOf) {
   HandleScope handle_scope(isolate);
   return String::LastIndexOf(isolate, args.receiver(),
                              args.atOrUndefined(isolate, 1),
                              args.atOrUndefined(isolate, 2));
 }
 
 // ES6 section 21.1.3.10 String.prototype.localeCompare ( that )
@@ skipping 121 matching lines @@
   Node* receiver = assembler->Parameter(0);
   Node* context = assembler->Parameter(3);
 
   Node* result = assembler->ToThisValue(
       context, receiver, PrimitiveType::kString, "String.prototype.valueOf");
   assembler->Return(result);
 }
 
 }  // namespace internal
 }  // namespace v8