Add a feature flag for network service and about:flags entry for it.

content/public/common/browser_side_navigation_policy.cc

Index: content/public/common/browser_side_navigation_policy.cc
diff --git a/content/public/common/browser_side_navigation_policy.cc b/content/public/common/browser_side_navigation_policy.cc
index 698ce3f3a69450e2d07056ddd4c6f008192b8ebe..67f2ccb9c74224eaa2fae1c7cf34ea057b4067df 100644
--- a/content/public/common/browser_side_navigation_policy.cc
+++ b/content/public/common/browser_side_navigation_policy.cc
@@ -11,10 +11,10 @@
 namespace content {
 
 bool IsBrowserSideNavigationEnabled() {
-  return
-      base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableBrowserSideNavigation) ||
-      base::FeatureList::IsEnabled(features::kBrowserSideNavigation);
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(
+             switches::kEnableBrowserSideNavigation) ||
+         base::FeatureList::IsEnabled(features::kBrowserSideNavigation) ||
+         base::FeatureList::IsEnabled(features::kNetworkService);

[Alexei Svitkine (slow), 2017/06/29 13:58:24]

Shouldn't this be () && net enabled?

Otherwise, it will enable browser side navigation even if kBrowserSideNavigation
is not enabled.

(Separately, could we also remove switches::kEnableBrowserSideNavigation since
there's a feature?)

[jam, 2017/06/30 17:21:18]

Yep that's the intended behavior. Network Service depends on MojoLoading and
BrowserSideNavigation.
This is historical before the feature and is used by bots and locally be devs.
PlzNavigate will get turned on soon, so we'll take both out then.

 }
 
 }  // namespace content