Introduce Origin-Trial for Service Worker Navigation Preload

content/child/runtime_features.cc

 // Copyright 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.
 
 #include "content/child/runtime_features.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/feature_list.h"
@@ skipping 296 matching lines @@
     WebRuntimeFeatures::enableSendBeaconThrowForBlobWithNonSimpleType(true);
 
 #if defined(OS_ANDROID)
   if (command_line.HasSwitch(switches::kDisableMediaSessionAPI))
     WebRuntimeFeatures::enableMediaSession(false);
 
   WebRuntimeFeatures::enablePaymentRequest(
       base::FeatureList::IsEnabled(features::kWebPayments));
 #endif
 
-  if (base::FeatureList::IsEnabled(features::kServiceWorkerNavigationPreload))
+  // We set the RuntimeEnabledFeatures for Navigation Preload feature only when
+  // it is set by "--enable-features" flag.
+  // While we are experimenting this feature using Origin Trial, we enable this
+  // feature using the field trial mechanism. So FeatureList::IsEnabled() always
+  // returns true. But, unless the command line explicitly enabled the feature,
+  // this feature should be available only when an valid origin trial token is

[clamy, 2017/01/13 17:44:09]

nit: s/an/a

[horo, 2017/01/13 23:01:24]

Done.

+  // set. This check is done by the generated code of
+  // blink::OriginTrials::serviceWorkerNavigationPreloadEnabled(). See the
+  // comments in service_worker_version.h for the details.
+  if (base::FeatureList::GetInstance()->IsFeatureOverriddenFromCommandLine(
+          features::kServiceWorkerNavigationPreload.name,
+          base::FeatureList::OVERRIDE_ENABLE_FEATURE)) {
     WebRuntimeFeatures::enableServiceWorkerNavigationPreload(true);
+  }
 
   if (base::FeatureList::IsEnabled(features::kSpeculativeLaunchServiceWorker))
     WebRuntimeFeatures::enableSpeculativeLaunchServiceWorker(true);
 
   if (base::FeatureList::IsEnabled(features::kGamepadExtensions))
     WebRuntimeFeatures::enableGamepadExtensions(true);
 
   if (!base::FeatureList::IsEnabled(features::kCompositeOpaqueFixedPosition))
     WebRuntimeFeatures::enableFeatureFromString("CompositeOpaqueFixedPosition",
         false);
@@ skipping 26 matching lines @@
   if (command_line.HasSwitch(switches::kDisableBlinkFeatures)) {
     std::vector<std::string> disabled_features = base::SplitString(
         command_line.GetSwitchValueASCII(switches::kDisableBlinkFeatures),
         ",", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
     for (const std::string& feature : disabled_features)
       WebRuntimeFeatures::enableFeatureFromString(feature, false);
   }
 }
 
 }  // namespace content