Rename iterator debugging flag in GN.

build/config/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/module_args/v8.gni")
 import("//build/toolchain/goma.gni")
 
 declare_args() {
-  # When set, turns off the (normally-on) iterator debugging and related stuff
-  # that is normally turned on for Debug builds. These are generally useful for
-  # catching bugs but in some cases may cause conflicts or excessive slowness.
-  disable_iterator_debugging = false
+  # When set (the default) enables C++ iterator debugging in debug builds.
+  # Iterator debugging is always off in release builds (technically, this flag
+  # affects the "debug" config, which is always available but applied by
+  # default only in debug builds).
+  #
+  # Iterator debugging is generally useful for catching bugs. But it can
+  # introduce extra locking to check the state of an iterator against the state
+  # of the current object. For iterator- and thread-heavy code, this can
+  # significantly slow execution.
+  enable_iterator_debugging = true
 
   # Set to true to not store any build metadata, e.g. ifdef out all __DATE__
   # and __TIME__. Set to 0 to reenable the use of these macros in the code
   # base. See http://crbug.com/314403.
   #
   # Continue to embed build meta data in Official builds, basically the
   # time it was built.
   # TODO(maruel): This decision should be revisited because having an
   # official deterministic build has high value too but MSVC toolset can't
   # generate anything deterministic with WPO enabled AFAIK.
@@ skipping 263 matching lines @@
     "_DEBUG",
     "DYNAMIC_ANNOTATIONS_ENABLED=1",
     "WTF_USE_DYNAMIC_ANNOTATIONS=1",
   ]
 
   if (is_nacl) {
     defines += [ "DYNAMIC_ANNOTATIONS_PREFIX=NACL_" ]
   }
 
   if (is_win) {
-    if (disable_iterator_debugging) {
-      # Iterator debugging is enabled by the compiler on debug builds, and we
-      # have to tell it to turn it off.
+    if (!enable_iterator_debugging) {
+      # Iterator debugging is enabled by default by the compiler on debug
+      # builds, and we have to tell it to turn it off.
       defines += [ "_HAS_ITERATOR_DEBUGGING=0" ]
     }
-  } else if (is_linux && !is_android && current_cpu == "x64" &&
-             !disable_iterator_debugging) {
+  } else if (is_linux && current_cpu == "x64" && enable_iterator_debugging) {
     # Enable libstdc++ debugging facilities to help catch problems early, see
     # http://crbug.com/65151 .
     # TODO(phajdan.jr): Should we enable this for all of POSIX?
     defines += [ "_GLIBCXX_DEBUG=1" ]
   }
 }
 
 config("release") {
   defines = [ "NDEBUG" ]
 
@@ skipping 118 matching lines @@
     # with precompiled headers since the source file that's "compiled" for
     # making the precompiled header is empty.
     #
     # This error doesn't happen every time. In VS2013, it seems if the .pch
     # file doesn't exist, no error will be generated (probably MS tested this
     # case but forgot the other one?). To reproduce this error, do a build,
     # then delete the precompile.c.obj file, then build again.
     cflags_c = [ "/wd4206" ]
   }
 }