Introduce incognito preference settings.

net/base/network_config_watcher_mac.cc

Index: net/base/network_config_watcher_mac.cc
diff --git a/net/base/network_config_watcher_mac.cc b/net/base/network_config_watcher_mac.cc
index afec17d91f4eeccaaf4a59cd27143174e65b5f74..857dc0f4934374c1a18669e5224abed04a35805c 100644
--- a/net/base/network_config_watcher_mac.cc
+++ b/net/base/network_config_watcher_mac.cc
@@ -10,6 +10,7 @@
 
 #include "base/compiler_specific.h"
 #include "base/threading/thread.h"
+#include "base/threading/thread_restrictions.h"
 #include "base/mac/scoped_cftyperef.h"
 
 namespace net {
@@ -54,10 +55,17 @@ NetworkConfigWatcherMacThread::NetworkConfigWatcherMacThread(
       ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {}
 
 NetworkConfigWatcherMacThread::~NetworkConfigWatcherMacThread() {
-  Stop();
+  // As nothing in this thread is allowed to perform blocking I/O
+  // we are save to permit this for the thread's termination.
+  {
+    base::ThreadRestrictions::ScopedAllowIO allow_io;
+    Stop();
+  }
 }
 
 void NetworkConfigWatcherMacThread::Init() {
+  base::ThreadRestrictions::SetIOAllowed(false);
+
   // TODO(willchan): Look to see if there's a better signal for when it's ok to
   // initialize this, rather than just delaying it by a fixed time.
   const int kInitializationDelayMS = 1000;