[regexp] Let RegExp.prototype.compile return this

src/builtins/builtins-regexp.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-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/regexp/jsregexp.h"
 #include "src/regexp/regexp-utils.h"
@@ skipping 834 matching lines @@
     Node* const new_flags = FlagsGetter(context, pattern, true);
     Node* const new_pattern = LoadObjectField(pattern, JSRegExp::kSourceOffset);
 
     var_flags.Bind(new_flags);
     var_pattern.Bind(new_pattern);
 
     Goto(&next);
     Bind(&next);
   }
 
-  RegExpInitialize(context, receiver, var_pattern.value(), var_flags.value());
-
-  // Return undefined for compatibility with JSC.
-  // See http://crbug.com/585775 for web compat details.
-
-  Return(UndefinedConstant());
+  Node* const result = RegExpInitialize(context, receiver, var_pattern.value(),
+                                        var_flags.value());
+  Return(result);
 }
 
 // ES6 21.2.5.10.
 TF_BUILTIN(RegExpPrototypeSourceGetter, RegExpBuiltinsAssembler) {
   Node* const receiver = Parameter(0);
   Node* const context = Parameter(3);
 
   // Check whether we have an unmodified regexp instance.
   Label if_isjsregexp(this), if_isnotjsregexp(this, Label::kDeferred);
 
@@ skipping 1675 matching lines @@
   Bind(&if_matched);
   {
     Node* result =
         ConstructNewResultFromMatchInfo(context, match_indices, string);
     Return(result);
   }
 }
 
 }  // namespace internal
 }  // namespace v8