Add an optional source length field to the Extension constructor.

src/serialize.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1402 matching lines @@
 
 void Serializer::ObjectSerializer::VisitExternalAsciiString(
     v8::String::ExternalAsciiStringResource** resource_pointer) {
   Address references_start = reinterpret_cast<Address>(resource_pointer);
   OutputRawData(references_start);
   for (int i = 0; i < Natives::GetBuiltinsCount(); i++) {
     Object* source = HEAP->natives_source_cache()->get(i);
     if (!source->IsUndefined()) {
       ExternalAsciiString* string = ExternalAsciiString::cast(source);
       typedef v8::String::ExternalAsciiStringResource Resource;
-      Resource* resource = string->resource();
+      const Resource* resource = string->resource();
       if (resource == *resource_pointer) {
         sink_->Put(kNativesStringResource, "NativesStringResource");
         sink_->PutSection(i, "NativesStringResourceEnd");
         bytes_processed_so_far_ += sizeof(resource);
         return;
       }
     }
   }
   // One of the strings in the natives cache should match the resource.  We
   // can't serialize any other kinds of external strings.
@@ skipping 90 matching lines @@
       fullness_[space] = RoundUp(fullness_[space], Page::kPageSize);
     }
   }
   int allocation_address = fullness_[space];
   fullness_[space] = allocation_address + size;
   return allocation_address;
 }
 
 
 } }  // namespace v8::internal