Introduce "optimized_out" oddball marker for compilers.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 5cdfa9a219aa530b17c48b73463a0c6b762b0468..b39bd81ffd4c14b4245dbd0041353fbc32a75001 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -2329,6 +2329,7 @@ bool Heap::CreateInitialMaps() {
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, no_interceptor_result_sentinel);
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, exception);
     ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, termination_exception);
+    ALLOCATE_MAP(ODDBALL_TYPE, Oddball::kSize, optimized_out);
 
     for (unsigned i = 0; i < arraysize(string_type_table); i++) {
       const StringTypeTable& entry = string_type_table[i];
@@ -2700,6 +2701,11 @@ void Heap::CreateInitialObjects() {
                                      handle(Smi::FromInt(-5), isolate()), false,
                                      "undefined", Oddball::kException));
 
+  set_optimized_out(
+      *factory->NewOddball(factory->optimized_out_map(), "optimized_out",
+                           handle(Smi::FromInt(-6), isolate()), false,
+                           "undefined", Oddball::kOptimizedOut));
+
   for (unsigned i = 0; i < arraysize(constant_string_table); i++) {
     Handle<String> str =
         factory->InternalizeUtf8String(constant_string_table[i].contents);