Add filler at the new space top when forcing scavenge.

test/cctest/test-symbols.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 
 // Check that we can traverse very deep stacks of ConsStrings using
 // StringCharacterStram.  Check that Get(int) works on very deep stacks
 // of ConsStrings.  These operations may not be very fast, but they
 // should be possible without getting errors due to too deep recursion.
 
 #include "v8.h"
 
 #include "cctest.h"
@@ skipping 19 matching lines @@
     symbols[i]->ShortPrint();
     PrintF("\n");
 #if OBJECT_PRINT
     symbols[i]->Print();
 #endif
 #if VERIFY_HEAP
     symbols[i]->Verify();
 #endif
   }
 
-  CcTest::heap()->PerformScavenge();
+  CcTest::heap()->CollectGarbage(i::NEW_SPACE);
   CcTest::heap()->CollectAllGarbage(Heap::kNoGCFlags);
 
   // All symbols should be distinct.
   for (int i = 0; i < kNumSymbols; ++i) {
     CHECK(symbols[i]->SameValue(*symbols[i]));
     for (int j = i + 1; j < kNumSymbols; ++j) {
       CHECK(!symbols[i]->SameValue(*symbols[j]));
     }
   }
 }