Reland "Handlify concat string and substring."

src/heap.h

 // Copyright 2012 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 1053 matching lines @@
   // Please note that this does not perform a garbage collection.
   MUST_USE_RESULT MaybeObject* AllocateJSMessageObject(
       String* type,
       JSArray* arguments,
       int start_position,
       int end_position,
       Object* script,
       Object* stack_trace,
       Object* stack_frames);
 
-  // Allocates a new cons string object.
-  // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
-  // failed.
-  // Please note this does not perform a garbage collection.
-  MUST_USE_RESULT MaybeObject* AllocateConsString(String* first,
-                                                  String* second);
-
-  // Allocates a new sub string object which is a substring of an underlying
-  // string buffer stretching from the index start (inclusive) to the index
-  // end (exclusive).
-  // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
-  // failed.
-  // Please note this does not perform a garbage collection.
-  MUST_USE_RESULT MaybeObject* AllocateSubString(
-      String* buffer,
-      int start,
-      int end,
-      PretenureFlag pretenure = NOT_TENURED);
-
   // Allocate a new external string object, which is backed by a string
   // resource that resides outside the V8 heap.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
   MUST_USE_RESULT MaybeObject* AllocateExternalStringFromAscii(
       const ExternalAsciiString::Resource* resource);
   MUST_USE_RESULT MaybeObject* AllocateExternalStringFromTwoByte(
       const ExternalTwoByteString::Resource* resource);
 
@@ skipping 1977 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_