Reland of Enable RL by default

Reland of https://codereview.chromium.org/2562643003/ after fixing the
issue.

BUG=577659

Review-Url: https://codereview.chromium.org/2573473002
Cr-Commit-Position: refs/heads/master@{#438100}

components/reading_list/core/BUILD.gn

@@ -2,12 +2,22 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
+import("//components/reading_list/core/reading_list.gni")
+
 source_set("core") {
   sources = [
     "reading_list_switches.cc",
     "reading_list_switches.h",
   ]
   deps = [
+    ":reading_list_enable_flags",
     "//base",
   ]
 }
+
+buildflag_header("reading_list_enable_flags") {
+  header = "reading_list_enable_flags.h"
+  _enabled = is_ios && enable_reading_list
+  flags = [ "ENABLE_READING_LIST=$_enabled" ]
+}

components/reading_list/core/reading_list.gni

+# Copyright 2016 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.
+
+declare_args() {
+  # Controls whether reading list support is active or not. Currently only
+  # supported on iOS (on other platforms, the feature is always disabled).
+  enable_reading_list = true
+}

components/reading_list/core/reading_list_switches.cc

@@ -6,23 +6,12 @@
 
 #include "build/build_config.h"
 #include "base/command_line.h"
+#include "components/reading_list/core/reading_list_enable_flags.h"
 
 namespace reading_list {
 namespace switches {
-// Enables the reading list.
-const char kEnableReadingList[] = "enable-reading-list";
-
-// Disables the reading list.
-const char kDisableReadingList[] = "disable-reading-list";
-
 bool IsReadingListEnabled() {
-  // Reading list is only enabled on iOS.
-#if defined(OS_IOS)
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(kEnableReadingList)) {
-    return true;
-  }
-#endif
-  return false;
+  return BUILDFLAG(ENABLE_READING_LIST);
 }
 }  // namespace switches
 }  // namespace reading_list

components/reading_list/core/reading_list_switches.h

@@ -7,9 +7,6 @@
 
 namespace reading_list {
 namespace switches {
-extern const char kEnableReadingList[];
-extern const char kDisableReadingList[];
-
 // Whether Reading List is enabled on this device.
 bool IsReadingListEnabled();
 }  // namespace switches

ios/chrome/browser/about_flags.mm

@@ -234,13 +234,6 @@ void AppendSwitchesFromExperimentalSettings(base::CommandLine* command_line) {
     command_line->AppendSwitch(switches::kDisablePaymentRequest);
   }
 
-  // Populate command line flags from Reading List.
-  if ([defaults boolForKey:@"EnableReadingList"]) {
-    command_line->AppendSwitch(reading_list::switches::kEnableReadingList);
-  } else {
-    command_line->AppendSwitch(reading_list::switches::kDisableReadingList);
-  }
-
   // Populate command line flag for Spotlight Actions.
   if ([defaults boolForKey:@"DisableSpotlightActions"]) {
     command_line->AppendSwitch(switches::kDisableSpotlightActions);

ios/chrome/browser/sync/BUILD.gn

@@ -112,6 +112,7 @@ source_set("unit_tests") {
     ":sync",
     "//base",
     "//components/browser_sync",
+    "//components/reading_list/core",
     "//components/sync",
     "//ios/chrome/browser/browser_state:test_support",
     "//ios/web:test_support",

ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory_unittest.cc

@@ -12,6 +12,7 @@
 #include "base/macros.h"
 #include "components/browser_sync/browser_sync_switches.h"
 #include "components/browser_sync/profile_sync_service.h"
+#include "components/reading_list/core/reading_list_switches.h"
 #include "components/sync/base/model_type.h"
 #include "components/sync/driver/data_type_controller.h"
 #include "ios/chrome/browser/browser_state/test_chrome_browser_state.h"
@@ -45,6 +46,9 @@ class IOSChromeProfileSyncServiceFactoryTest : public testing::Test {
     datatypes.push_back(syncer::PASSWORDS);
     datatypes.push_back(syncer::PREFERENCES);
     datatypes.push_back(syncer::PRIORITY_PREFERENCES);
+    if (reading_list::switches::IsReadingListEnabled()) {
+      datatypes.push_back(syncer::READING_LIST);
+    }
     datatypes.push_back(syncer::SESSIONS);
     datatypes.push_back(syncer::PROXY_TABS);
     datatypes.push_back(syncer::TYPED_URLS);