Canonicalize handles for optimized compilation.

src/string-builder.h

 // Copyright 2014 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.
 
 #ifndef V8_STRING_BUILDER_H_
 #define V8_STRING_BUILDER_H_
 
 #include "src/assert-scope.h"
 #include "src/factory.h"
 #include "src/handles.h"
@@ skipping 328 matching lines @@
   };
 
   template <typename DestChar>
   class NoExtendString : public NoExtend<DestChar> {
    public:
     NoExtendString(Handle<String> string, int required_length)
         : NoExtend<DestChar>(string, 0), string_(string) {
       DCHECK(string->length() >= required_length);
     }
 
-    ~NoExtendString() {
+    Handle<String> Finalize() {
       Handle<SeqString> string = Handle<SeqString>::cast(string_);
       int length = NoExtend<DestChar>::written();
-      *string_.location() = *SeqString::Truncate(string, length);
+      Handle<String> result = SeqString::Truncate(string, length);
+      string_ = Handle<String>();
+      return result;
     }
 
    private:
     Handle<String> string_;
   };
 
   template <typename DestChar>
   class NoExtendBuilder : public NoExtend<DestChar> {
    public:
     NoExtendBuilder(IncrementalStringBuilder* builder, int required_length)
@@ skipping 63 matching lines @@
     DCHECK_EQ(String::TWO_BYTE_ENCODING, encoding_);
     SeqTwoByteString::cast(*current_part_)
         ->SeqTwoByteStringSet(current_index_++, c);
   }
   if (current_index_ == part_length_) Extend();
 }
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_STRING_BUILDER_H_