[runtime] Use "the hole" instead of smi 0 as sentinel for context extension.

src/runtime/runtime-debug.cc

 // Copyright 2014 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/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/debug/debug.h"
 #include "src/debug/debug-evaluate.h"
 #include "src/debug/debug-frames.h"
@@ skipping 1262 matching lines @@
   // Check the execution state and decode arguments frame and source to be
   // evaluated.
   DCHECK(args.length() == 6);
   CONVERT_NUMBER_CHECKED(int, break_id, Int32, args[0]);
   RUNTIME_ASSERT(isolate->debug()->CheckExecutionState(break_id));
 
   CONVERT_SMI_ARG_CHECKED(wrapped_id, 1);
   CONVERT_NUMBER_CHECKED(int, inlined_jsframe_index, Int32, args[2]);
   CONVERT_ARG_HANDLE_CHECKED(String, source, 3);
   CONVERT_BOOLEAN_ARG_CHECKED(disable_break, 4);
-  CONVERT_ARG_HANDLE_CHECKED(Object, context_extension, 5);
+  CONVERT_ARG_HANDLE_CHECKED(HeapObject, context_extension, 5);
 
   StackFrame::Id id = DebugFrameHelper::UnwrapFrameId(wrapped_id);
 
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       DebugEvaluate::Local(isolate, id, inlined_jsframe_index, source,
                            disable_break, context_extension));
   return *result;
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugEvaluateGlobal) {
   HandleScope scope(isolate);
 
   // Check the execution state and decode arguments frame and source to be
   // evaluated.
   DCHECK(args.length() == 4);
   CONVERT_NUMBER_CHECKED(int, break_id, Int32, args[0]);
   RUNTIME_ASSERT(isolate->debug()->CheckExecutionState(break_id));
 
   CONVERT_ARG_HANDLE_CHECKED(String, source, 1);
   CONVERT_BOOLEAN_ARG_CHECKED(disable_break, 2);
-  CONVERT_ARG_HANDLE_CHECKED(Object, context_extension, 3);
+  CONVERT_ARG_HANDLE_CHECKED(HeapObject, context_extension, 3);
 
   Handle<Object> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, result,
       DebugEvaluate::Global(isolate, source, disable_break, context_extension));
   return *result;
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugGetLoadedScripts) {
@@ skipping 393 matching lines @@
   return *isolate->factory()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugBreakInOptimizedCode) {
   UNIMPLEMENTED();
   return NULL;
 }
 }  // namespace internal
 }  // namespace v8