Add ES2015 RegExp full subclassing semantics behind a flag

src/messages.h

 // Copyright 2006-2008 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.
 
 // The infrastructure used for (localized) message reporting in V8.
 //
 // Note: there's a big unresolved issue about ownership of the data
 // structures used by this framework.
 
 #ifndef V8_MESSAGES_H_
@@ skipping 118 matching lines @@
   T(FunctionBind, "Bind must be called on a function")                         \
   T(GeneratorRunning, "Generator is already running")                          \
   T(IllegalInvocation, "Illegal invocation")                                   \
   T(IncompatibleMethodReceiver, "Method % called on incompatible receiver %")  \
   T(InstanceofFunctionExpected,                                                \
     "Expecting a function in instanceof check, but got %")                     \
   T(InstanceofNonobjectProto,                                                  \
     "Function has non-object prototype '%' in instanceof check")               \
   T(InvalidArgument, "invalid_argument")                                       \
   T(InvalidInOperatorUse, "Cannot use 'in' operator to search for '%' in %")   \
+  T(InvalidRegExpExecResult,                                                   \
+    "RegExp exec method returned something other than an Object or null")      \
   T(InvalidSimdOperation, "% is not a valid type for this SIMD operation.")    \
   T(IteratorResultNotAnObject, "Iterator result % is not an object")           \
   T(IteratorValueNotAnObject, "Iterator value % is not an entry object")       \
   T(LanguageID, "Language ID should be string or object.")                     \
   T(MethodCalledOnWrongObject,                                                 \
     "Method % called on a non-object or on a wrong type of object.")           \
   T(MethodInvokedOnNullOrUndefined,                                            \
     "Method invoked on undefined or null value.")                              \
   T(MethodInvokedOnWrongType, "Method invoked on an object that is not %.")    \
   T(NoAccess, "no access")                                                     \
@@ skipping 363 matching lines @@
   static Handle<String> GetMessage(Isolate* isolate, Handle<Object> data);
   static base::SmartArrayPointer<char> GetLocalizedMessage(Isolate* isolate,
                                                            Handle<Object> data);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_MESSAGES_H_