[debug,api] Do not use embedder field for debug context id.

src/contexts.h

 // Copyright 2012 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.
 
 #ifndef V8_CONTEXTS_H_
 #define V8_CONTEXTS_H_
 
 #include "src/heap/heap.h"
 #include "src/objects.h"
 
@@ skipping 223 matching lines @@
     bound_function_without_constructor_map)                                    \
   V(CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, JSFunction,                            \
     call_as_constructor_delegate)                                              \
   V(CALL_AS_FUNCTION_DELEGATE_INDEX, JSFunction, call_as_function_delegate)    \
   V(CALLSITE_FUNCTION_INDEX, JSFunction, callsite_function)                    \
   V(CONTEXT_EXTENSION_FUNCTION_INDEX, JSFunction, context_extension_function)  \
   V(CURRENT_MODULE_INDEX, Module, current_module)                              \
   V(DATA_PROPERTY_DESCRIPTOR_MAP_INDEX, Map, data_property_descriptor_map)     \
   V(DATA_VIEW_FUN_INDEX, JSFunction, data_view_fun)                            \
   V(DATE_FUNCTION_INDEX, JSFunction, date_function)                            \
+  V(DEBUG_CONTEXT_ID_INDEX, Object, debug_context_id)                          \
   V(ERROR_MESSAGE_FOR_CODE_GEN_FROM_STRINGS_INDEX, Object,                     \
     error_message_for_code_gen_from_strings)                                   \
   V(ERRORS_THROWN_INDEX, Smi, errors_thrown)                                   \
   V(EXTRAS_EXPORTS_OBJECT_INDEX, JSObject, extras_binding_object)              \
   V(EXTRAS_UTILS_OBJECT_INDEX, Object, extras_utils_object)                    \
   V(FAST_ALIASED_ARGUMENTS_MAP_INDEX, Map, fast_aliased_arguments_map)         \
   V(FAST_TEMPLATE_INSTANTIATIONS_CACHE_INDEX, FixedArray,                      \
     fast_template_instantiations_cache)                                        \
   V(FLOAT32_ARRAY_FUN_INDEX, JSFunction, float32_array_fun)                    \
   V(FLOAT64_ARRAY_FUN_INDEX, JSFunction, float64_array_fun)                    \
@@ skipping 470 matching lines @@
   STATIC_ASSERT(kHeaderSize == Internals::kContextHeaderSize);
   STATIC_ASSERT(EMBEDDER_DATA_INDEX == Internals::kContextEmbedderDataIndex);
 };
 
 typedef Context::Field ContextField;
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CONTEXTS_H_