[debugger] simplify debug stepping.

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 1047 matching lines @@
   static ExternalReference invoke_function_callback(Isolate* isolate);
   static ExternalReference invoke_accessor_getter_callback(Isolate* isolate);
 
   static ExternalReference virtual_handler_register(Isolate* isolate);
   static ExternalReference virtual_slot_register(Isolate* isolate);
 
   static ExternalReference runtime_function_table_address(Isolate* isolate);
 
   Address address() const { return reinterpret_cast<Address>(address_); }
 
-  // Used to check if single stepping is enabled in generated code.
-  static ExternalReference debug_step_in_enabled_address(Isolate* isolate);
+  // Used to read out the last step action of the debugger.
+  static ExternalReference debug_last_step_action_address(Isolate* isolate);
 
   // Used to check for suspended generator, used for stepping across await call.
   static ExternalReference debug_suspended_generator_address(Isolate* isolate);
 
 #ifndef V8_INTERPRETED_REGEXP
   // C functions called from RegExp generated code.
 
   // Function NativeRegExpMacroAssembler::CaseInsensitiveCompareUC16()
   static ExternalReference re_case_insensitive_compare_uc16(Isolate* isolate);
 
@@ skipping 260 matching lines @@
     std::vector<ConstantPoolEntry> shared_entries;
   };
 
   Label emitted_label_;  // Records pc_offset of emitted pool
   PerTypeEntryInfo info_[ConstantPoolEntry::NUMBER_OF_TYPES];
 };
 
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_ASSEMBLER_H_