Implemented one-char cache lookup in generated code.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 524e8e23d4c0c427e5fb02cc8a00bf69b2331d17..7ba6a5f7aa3f9a67e348363538c7001c6c8f5a50 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -1655,7 +1655,7 @@ bool Heap::CreateInitialObjects() {
   if (InitializeNumberStringCache()->IsFailure()) return false;
 
   // Allocate cache for single character strings.
-  obj = AllocateFixedArray(String::kMaxAsciiCharCode+1);
+  obj = AllocateFixedArray(String::kMaxAsciiCharCode+1, TENURED);
   if (obj->IsFailure()) return false;
   set_single_character_string_cache(FixedArray::cast(obj));