[turbofan] Modifies the --turbo-verify-machine-graph flag to act as a filter.

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 432 matching lines @@
 DEFINE_BOOL(trace_turbo_scheduler, false, "trace TurboFan's scheduler")
 DEFINE_BOOL(trace_turbo_reduction, false, "trace TurboFan's various reducers")
 DEFINE_BOOL(trace_turbo_trimming, false, "trace TurboFan's graph trimmer")
 DEFINE_BOOL(trace_turbo_jt, false, "trace TurboFan's jump threading")
 DEFINE_BOOL(trace_turbo_ceq, false, "trace TurboFan's control equivalence")
 DEFINE_BOOL(trace_turbo_loop, false, "trace TurboFan's loop optimizations")
 DEFINE_BOOL(turbo_asm, true, "enable TurboFan for asm.js code")
 DEFINE_BOOL(turbo_asm_deoptimization, false,
             "enable deoptimization in TurboFan for asm.js code")
 DEFINE_BOOL(turbo_verify, DEBUG_BOOL, "verify TurboFan graphs at each phase")
-DEFINE_BOOL(turbo_verify_machine_graph, false,
-            "verify TurboFan machine graph before instruction selection")
+DEFINE_STRING(turbo_verify_machine_graph, nullptr,
+              "verify TurboFan machine graph before instruction selection")
 DEFINE_BOOL(turbo_stats, false, "print TurboFan statistics")
 DEFINE_BOOL(turbo_stats_nvp, false,
             "print TurboFan statistics in machine-readable format")
 DEFINE_BOOL(turbo_splitting, true, "split nodes during scheduling in TurboFan")
 DEFINE_BOOL(turbo_type_feedback, true,
             "use typed feedback for representation inference in Turbofan")
 DEFINE_BOOL(turbo_source_positions, false,
             "track source code positions when building TurboFan IR")
 DEFINE_IMPLICATION(trace_turbo, turbo_source_positions)
 DEFINE_BOOL(function_context_specialization, false,
@@ skipping 748 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