Fix tests that fail on GC stress tests.

test/cctest/test-strings.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 1065 matching lines @@
   Handle<String> string =
       FACTORY->NewStringFromAscii(CStrVector("parentparentparent"));
   Handle<String> parent = FACTORY->NewConsString(string, string);
   CHECK(parent->IsConsString());
   CHECK(!parent->IsFlat());
   Handle<String> slice = FACTORY->NewSubString(parent, 1, 25);
   // After slicing, the original string becomes a flat cons.
   CHECK(parent->IsFlat());
   CHECK(slice->IsSlicedString());
   CHECK_EQ(SlicedString::cast(*slice)->parent(),
-           ConsString::cast(*parent)->first());
+           // Parent could have been short-circuited.
+           parent->IsConsString() ? ConsString::cast(*parent)->first()
+                                  : *parent);
   CHECK(SlicedString::cast(*slice)->parent()->IsSeqString());
   CHECK(slice->IsFlat());
 }
 
 
 class AsciiVectorResource : public v8::String::ExternalAsciiStringResource {
  public:
   explicit AsciiVectorResource(i::Vector<const char> vector)
       : data_(vector) {}
   virtual ~AsciiVectorResource() {}
@@ skipping 251 matching lines @@
       CheckCanonicalEquivalence(c, test);
       continue;
     }
     if (upper != c && lower != c) {
       CheckCanonicalEquivalence(c, test);
       continue;
     }
     CHECK_EQ(Min(upper, lower), test);
   }
 }