Use feature architecture as kill switch for WebAPKs instead of field trial

chrome/browser/android/chrome_feature_list.cc

 // Copyright 2015 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 "chrome/browser/android/chrome_feature_list.h"
 
 #include <stddef.h>
 
 #include <string>
 
@@ skipping 33 matching lines @@
     &ntp_snippets::kSaveToOfflineFeature,
     &ntp_snippets::kSectionDismissalFeature,
     &kNTPFakeOmniboxTextFeature,
     &kNTPOfflinePagesFeature,
     &kPhysicalWebFeature,
     &kPhysicalWebIgnoreOtherClientsFeature,
     &kScanCardsInWebPayments,
     &kSpecialLocaleFeature,
     &kSpecialLocaleWrapper,
     &kTabReparenting,
+    &kWebApk,
     &kCCTExternalLinkHandling,
     &offline_pages::kOfflinePagesBackgroundLoadingFeature,
     &offline_pages::kBackgroundLoaderForDownloadsFeature,
     &offline_pages::kOfflinePagesCTFeature,  // See crbug.com/620421.
     &offline_pages::kOfflinePagesSharingFeature,
     &password_manager::features::kViewPasswords,
 };
 
 }  // namespace
 
@@ skipping 32 matching lines @@
 
 const base::Feature kTabReparenting{"TabReparenting",
                                     base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kCCTExternalLinkHandling{"CCTExternalLinkHandling",
                                     base::FEATURE_ENABLED_BY_DEFAULT};
 
 const base::Feature kUserMediaScreenCapturing{
     "UserMediaScreenCapturing", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Makes "Add to Home screen" in the app menu generate an APK for the shortcut
+// URL which opens Chrome in fullscreen.
+// For WebAPKs to be enabled, the WebAPK feature must be enabled and the

[dominickn, 2016/10/24 04:04:17]

Is it strictly necessary for the feature to be enabled and --enable-webapk to be
specified as well?

I believe you should be able to make the --enable-webapk flag enable this
feature, so you can probably remove the final two lines of this comment. 
Disabled features should take precedence over enabled features, so if you
kill-switch WebAPKs via Finch the disable should win even if the flag is on.

+// --enable-webapk command line flag must be set.
+const base::Feature kWebApk{"WebAPK", base::FEATURE_ENABLED_BY_DEFAULT};
+
 static jboolean IsEnabled(JNIEnv* env,
                           const JavaParamRef<jclass>& clazz,
                           const JavaParamRef<jstring>& jfeature_name) {
   const std::string feature_name = ConvertJavaStringToUTF8(env, jfeature_name);
   for (size_t i = 0; i < arraysize(kFeaturesExposedToJava); ++i) {
     if (kFeaturesExposedToJava[i]->name == feature_name)
       return base::FeatureList::IsEnabled(*kFeaturesExposedToJava[i]);
   }
   // Features queried via this API must be present in |kFeaturesExposedToJava|.
   NOTREACHED();
   return false;
 }
 
 bool RegisterChromeFeatureListJni(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace android
 }  // namespace chrome