[refactor] Separate generated builtins and C++ builtins into separate files

src/builtins/builtins-symbol-gen.cc

+// Copyright 2017 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-utils-gen.h"
+#include "src/builtins/builtins.h"
+#include "src/code-stub-assembler.h"
+
+namespace v8 {
+namespace internal {
+
+// -----------------------------------------------------------------------------
+// ES6 section 19.4 Symbol Objects
+
+// ES6 section 19.4.3.4 Symbol.prototype [ @@toPrimitive ] ( hint )
+TF_BUILTIN(SymbolPrototypeToPrimitive, CodeStubAssembler) {
+  Node* receiver = Parameter(0);
+  Node* context = Parameter(4);
+
+  Node* result = ToThisValue(context, receiver, PrimitiveType::kSymbol,
+                             "Symbol.prototype [ @@toPrimitive ]");
+  Return(result);
+}
+
+// ES6 section 19.4.3.2 Symbol.prototype.toString ( )
+TF_BUILTIN(SymbolPrototypeToString, CodeStubAssembler) {
+  Node* receiver = Parameter(0);
+  Node* context = Parameter(3);
+
+  Node* value = ToThisValue(context, receiver, PrimitiveType::kSymbol,
+                            "Symbol.prototype.toString");
+  Node* result = CallRuntime(Runtime::kSymbolDescriptiveString, context, value);
+  Return(result);
+}
+
+// ES6 section 19.4.3.3 Symbol.prototype.valueOf ( )
+TF_BUILTIN(SymbolPrototypeValueOf, CodeStubAssembler) {
+  Node* receiver = Parameter(0);
+  Node* context = Parameter(3);
+
+  Node* result = ToThisValue(context, receiver, PrimitiveType::kSymbol,
+                             "Symbol.prototype.valueOf");
+  Return(result);
+}
+
+}  // namespace internal
+}  // namespace v8