Avoid decoding overhead when allocating ascii strings....

src/heap.h

 // Copyright 2010 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 394 matching lines @@
   //   - ...FromTwoByte initializes the string from a buffer that is two-byte
   //     encoded.  If the characters are all single-byte characters, the
   //     result will be converted to ASCII, otherwise it will be left as
   //     two-byte.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this does not perform a garbage collection.
   MUST_USE_RESULT static MaybeObject* AllocateStringFromAscii(
       Vector<const char> str,
       PretenureFlag pretenure = NOT_TENURED);
-  MUST_USE_RESULT static MaybeObject* AllocateStringFromUtf8(
+  MUST_USE_RESULT static inline MaybeObject* AllocateStringFromUtf8(
+      Vector<const char> str,
+      PretenureFlag pretenure = NOT_TENURED);
+  MUST_USE_RESULT static MaybeObject* AllocateStringFromUtf8Slow(
       Vector<const char> str,
       PretenureFlag pretenure = NOT_TENURED);
   MUST_USE_RESULT static MaybeObject* AllocateStringFromTwoByte(
       Vector<const uc16> str,
       PretenureFlag pretenure = NOT_TENURED);
 
   // Allocates a symbol in old space based on the character stream.
   // Returns Failure::RetryAfterGC(requested_bytes, space) if the allocation
   // failed.
   // Please note this function does not perform a garbage collection.
@@ skipping 1683 matching lines @@
   // Return whether this object should be retained. If NULL is returned the
   // object has no references. Otherwise the address of the retained object
   // should be returned as in some GC situations the object has been moved.
   virtual Object* RetainAs(Object* object) = 0;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_