Removed a bunch of GetExistingThreadLocal calls by threading the Isolate.

src/runtime.cc

 // 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 3135 matching lines @@
     Handle<String> subject,
     Handle<JSRegExp> regexp,
     Handle<JSArray> last_match_info) {
   ASSERT(subject->IsFlat());
 
   bool is_global = regexp->GetFlags().is_global();
 
   // Shortcut for simple non-regexp global replacements
   if (is_global &&
       regexp->TypeTag() == JSRegExp::ATOM) {
-    Handle<String> empty_string(HEAP->empty_string());
+    Handle<String> empty_string = isolate->factory()->empty_string();
     if (subject->HasOnlyAsciiChars()) {
       return StringReplaceAtomRegExpWithString<SeqOneByteString>(
           isolate,
           subject,
           regexp,
           empty_string,
           last_match_info);
     } else {
       return StringReplaceAtomRegExpWithString<SeqTwoByteString>(
           isolate,
@@ skipping 10254 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal