Introduce "optimized_out" oddball marker for compilers.

src/debug/debug-frames.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/debug/debug-frames.h"
 
 #include "src/frames-inl.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 115 matching lines @@
     DCHECK(!value->IsTheHole());
 
     JSObject::SetOwnPropertyIgnoreAttributes(target, name, value, NONE).Check();
   }
 
   // Second fill all stack locals.
   for (int i = 0; i < scope_info->StackLocalCount(); ++i) {
     if (scope_info->LocalIsSynthetic(i)) continue;
     Handle<String> name(scope_info->StackLocalName(i));
     Handle<Object> value = GetExpression(scope_info->StackLocalIndex(i));
+    // TODO(yangguo): We convert optimized out values to {undefined} when they
+    // are passed to the debugger. Eventually we should handle them somehow.
     if (value->IsTheHole()) value = isolate_->factory()->undefined_value();
-
+    if (value->IsOptimizedOut()) value = isolate_->factory()->undefined_value();
     JSObject::SetOwnPropertyIgnoreAttributes(target, name, value, NONE).Check();
   }
 }
 
 
 void FrameInspector::MaterializeStackLocals(Handle<JSObject> target,
                                             Handle<JSFunction> function) {
   Handle<SharedFunctionInfo> shared(function->shared());
   Handle<ScopeInfo> scope_info(shared->scope_info());
   MaterializeStackLocals(target, scope_info);
@@ skipping 67 matching lines @@
       if (!frames[i].function()->shared()->IsSubjectToDebugging()) continue;
       if (++count == index) return i;
     }
   }
   return -1;
 }
 
 
 }  // namespace internal
 }  // namespace v8