[M118] Add emergency off-switch for GetNetworkConnectivityHint API

A previous CL added the call to GetNetworkConnectivityHint on
modern Windows systems, in order to function correctly inside
the sandbox.

This call makes subtle changes to the behavior of the network
change notifier, in particular it results in fewer incorrect
detections of online state, and more correct detections of
offline state.

As a precaution, place this new API call behind an
enabled-by-default emergency off-switch, just in case this has
any unexpected effects once it reaches Stable channel.

This CL contains no function change, since the feature is
enabled by default.

BUG=1450754

(cherry picked from commit 4bf4210)

Change-Id: I529bea07ee0a0a941574c04e0c2ca9440b72e33b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4903296
Commit-Queue: Will Harris <wfh@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1202977}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4908413
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Will Harris <wfh@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/branch-heads/5993@{#1069}
Cr-Branched-From: 5113507-refs/heads/main@{#1192594}

chrome/browser/net/sandboxed_network_change_notifier_win_browsertest.cc

@@ -33,6 +33,7 @@
 #include "content/public/browser/network_service_instance.h"
 #include "content/public/common/content_features.h"
 #include "content/public/test/browser_test.h"
+#include "net/base/features.h"
 #include "sandbox/policy/features.h"
 #include "services/network/public/mojom/network_change_manager.mojom.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -137,7 +138,10 @@ class SandboxedNetworkChangeNotifierBrowserTest
   SandboxedNetworkChangeNotifierBrowserTest() {
     if (GetParam()) {
       scoped_feature_list_.InitWithFeatures(
-          {sandbox::policy::features::kNetworkServiceSandbox},
+          {sandbox::policy::features::kNetworkServiceSandbox,
+           // When running inside the sandbox, the GetNetworkConnectivityHint
+           // API must be used.
+           net::features::kEnableGetNetworkConnectivityHintAPI},
           {features::kNetworkServiceInProcess});
     } else {
       scoped_feature_list_.InitWithFeatures(

net/base/features.cc

@@ -321,6 +321,10 @@ BASE_FEATURE(kBlockNewForbiddenHeaders,
 BASE_FEATURE(kPlatformKeyProbeSHA256,
              "PlatformKeyProbeSHA256",
              base::FEATURE_ENABLED_BY_DEFAULT);
+
+BASE_FEATURE(kEnableGetNetworkConnectivityHintAPI,
+             "EnableGetNetworkConnectivityHintAPI",
+             base::FEATURE_ENABLED_BY_DEFAULT);
 #endif
 
 // Prefetch to follow normal semantics instead of 5-minute rule

net/base/features.h

@@ -357,6 +357,10 @@ NET_EXPORT BASE_DECLARE_FEATURE(kBlockNewForbiddenHeaders);
 // Whether to probe for SHA-256 on some legacy platform keys, before assuming
 // the key requires SHA-1. See SSLPlatformKeyWin for details.
 NET_EXPORT BASE_DECLARE_FEATURE(kPlatformKeyProbeSHA256);
+
+// Whether or not to use the GetNetworkConnectivityHint API on modern Windows
+// versions for the Network Change Notifier.
+NET_EXPORT BASE_DECLARE_FEATURE(kEnableGetNetworkConnectivityHintAPI);
 #endif
 
 // Prefetch to follow normal semantics instead of 5-minute rule

net/base/network_change_notifier_win.cc

@@ -9,6 +9,7 @@
 
 #include <utility>
 
+#include "base/feature_list.h"
 #include "base/functional/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ -20,6 +21,7 @@
 #include "base/threading/thread.h"
 #include "base/time/time.h"
 #include "base/win/windows_version.h"
+#include "net/base/features.h"
 #include "net/base/winsock_init.h"
 #include "net/base/winsock_util.h"
 
@@ -241,7 +243,9 @@ NetworkChangeNotifierWin::RecomputeCurrentConnectionTypeModern() {
 // static
 NetworkChangeNotifier::ConnectionType
 NetworkChangeNotifierWin::RecomputeCurrentConnectionType() {
-  if (base::win::GetVersion() >= base::win::Version::WIN10_20H1) {
+  if (base::win::GetVersion() >= base::win::Version::WIN10_20H1 &&
+      base::FeatureList::IsEnabled(
+          features::kEnableGetNetworkConnectivityHintAPI)) {
     return RecomputeCurrentConnectionTypeModern();
   }