Add support for Dr memory in the GN build.

build/config/BUILD.gn

Index: build/config/BUILD.gn
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 216d0e9b17bec47133d3fbbf43d2ab08c2a84edb..7dabf019f59df5fb2285a82c2e4b2c17d1154808 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -3,11 +3,10 @@
 # found in the LICENSE file.
 
 declare_args() {
-  # When set, turns off the definition of _GLIBCXX_DEBUG when it would
-  # otherwise be set. Setting _GLIBCXX_DEBUG adds iterator debugging stuff
-  # that is usually helpful in debugging, but can cause problems in some
-  # contexts.
-  disable_glibcxx_debug = false
+  # When set, turns off the (normally-on) iterator debugging and related stuff
+  # that is normall turned on for Debug builds. These are generally useful for

[scottmg, 2014/01/17 23:52:25]

normally

+  # catching bugs but in some cases may cause conflicts or excessive slowness.
+  disable_iterator_debugging = false
 }
 
 config("my_msvs") {
@@ -46,7 +45,6 @@ config("my_msvs") {
 }
 
 config("feature_flags") {
-  #defines = 
 }
 
 config("debug") {
@@ -56,7 +54,14 @@ config("debug") {
     "WTF_USE_DYNAMIC_ANNOTATIONS=1",
   ]
 
-  if (is_linux && !is_android && cpu_arch == "x64" && !disable_glibcxx_debug) {
+  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.
+      defines += [ "_HAS_ITERATOR_DEBUGGING=0" ]
+    }
+  } else if (is_linux && !is_android && cpu_arch == "x64" &&
+             !disable_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?