Introduce --zap-cpp-pointers (off by default)

src/flag-definitions.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.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 1077 matching lines @@
 DEFINE_BOOL(print_builtin_ast, false, "print source AST for builtins")
 DEFINE_BOOL(trap_on_abort, false, "replace aborts by breakpoints")
 
 // compiler.cc
 DEFINE_BOOL(print_builtin_scopes, false, "print scopes for builtins")
 DEFINE_BOOL(print_scopes, false, "print scopes")
 
 // contexts.cc
 DEFINE_BOOL(trace_contexts, false, "trace contexts operations")
 
+// frames.cc
+DEFINE_BOOL(zap_cpp_pointers, false,
+            "zap heap pointers on the C++ stack during GC")
+
 // heap.cc
 DEFINE_BOOL(gc_verbose, false, "print stuff during garbage collection")
 DEFINE_BOOL(heap_stats, false, "report heap statistics before and after GC")
 DEFINE_BOOL(code_stats, false, "report code statistics after GC")
 DEFINE_BOOL(print_handles, false, "report handles after GC")
 DEFINE_BOOL(check_handle_count, false,
             "Check that there are not too many handles at GC")
 DEFINE_BOOL(print_global_handles, false, "report global handles after GC")
 
 // TurboFan debug-only flags.
@@ skipping 241 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA