[Tracing] Implement TracingCategoryObserver.

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 863 matching lines @@
             "(with snapshots this option cannot override the baked-in seed)")
 DEFINE_INT(hash_seed, 0,
            "Fixed seed to use to hash property keys (0 means random)"
            "(with snapshots this option cannot override the baked-in seed)")
 DEFINE_BOOL(trace_rail, false, "trace RAIL mode")
 DEFINE_BOOL(print_all_exceptions, false,
             "print exception object and stack trace on each thrown exception")
 
 // runtime.cc
 DEFINE_BOOL(runtime_call_stats, false, "report runtime call counts and times")
+DEFINE_INT(runtime_stats, 0,
+           "internal usage only for controlling runtime statistics")
+DEFINE_VALUE_IMPLICATION(runtime_call_stats, runtime_stats, 1)

[Camillo Bruni, 2016/10/21 08:20:55]

"runtime call stats" is by now probably an outdated name anyway :), so I'm all
in for --runtime-stats!

 
 // snapshot-common.cc
 DEFINE_BOOL(profile_deserialization, false,
             "Print the time it takes to deserialize the snapshot.")
 DEFINE_BOOL(serialization_statistics, false,
             "Collect statistics on serialized objects.")
 
 // Regexp
 DEFINE_BOOL(regexp_optimization, true, "generate optimized regexp code")
 
@@ skipping 319 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