[regexp] Properly flatten string during initialization

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 16093 matching lines @@
     }
     dst[d++] = src[s++];
   }
   DCHECK_EQ(result->length(), d);
   return result;
 }
 
 
 MaybeHandle<String> EscapeRegExpSource(Isolate* isolate,
                                        Handle<String> source) {
-  String::Flatten(source);
+  DCHECK(source->IsFlat());
   if (source->length() == 0) return isolate->factory()->query_colon_string();
   bool one_byte = source->IsOneByteRepresentationUnderneath();
   int escapes = one_byte ? CountRequiredEscapes<uint8_t>(source)
                          : CountRequiredEscapes<uc16>(source);
   if (escapes == 0) return source;
   int length = source->length() + escapes;
   if (one_byte) {
     Handle<SeqOneByteString> result;
     ASSIGN_RETURN_ON_EXCEPTION(isolate, result,
                                isolate->factory()->NewRawOneByteString(length),
@@ skipping 28 matching lines @@
 
 // static
 MaybeHandle<JSRegExp> JSRegExp::Initialize(Handle<JSRegExp> regexp,
                                            Handle<String> source, Flags flags) {
   Isolate* isolate = regexp->GetIsolate();
   Factory* factory = isolate->factory();
   // If source is the empty string we set it to "(?:)" instead as
   // suggested by ECMA-262, 5th, section 15.10.4.1.
   if (source->length() == 0) source = factory->query_colon_string();
 
+  source = String::Flatten(source);
+
   Handle<String> escaped_source;
   ASSIGN_RETURN_ON_EXCEPTION(isolate, escaped_source,
                              EscapeRegExpSource(isolate, source), JSRegExp);
 
   RETURN_ON_EXCEPTION(isolate, RegExpImpl::Compile(regexp, source, flags),
                       JSRegExp);
 
   regexp->set_source(*escaped_source);
   regexp->set_flags(Smi::FromInt(flags));
 
@@ skipping 4061 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8