Revert of Enable RL by default (patchset #6 id:100001 of...

Revert of Enable RL by default (patchset #6 id:100001 of https://codereview.chromium.org/2562643003/ )

Reason for revert:
Speculative revert as I think this CL broke the downstream autoroller.

It is a bit hard to debug as the autoroller was unable to land some CL as the downstream tree was closed, but the last successful roll would have happened at 39e086ae [1], and the first failing roll is at a229e828 [2].

This CL is the only one having an impact on the iOS build, so I think it is causing the failures:

$ git log --oneline 39e086ae...a229e828
a229e828 Strength-reduce the "scale-factor changed" condition in LayoutSVGRoot
d1693364 Update V8 to version 5.7.202.
7cfbed3d Enable RL by default
314c528d Revert of Improve EAT_STREAM_PARAMETERS for Windows x86 (patchset #10 id:240001 of https://codereview.chromium.org/2559323007/ )

[1]: https://uberchromegw.corp.google.com/i/internal.bling.main/builders/trunk-autoroller/builds/6861
[2]: https://uberchromegw.corp.google.com/i/internal.bling.main/builders/trunk-autoroller/builds/6862

Original issue's description:
> Enable RL by default
>
> BUG=577659
>
> Review-Url: https://codereview.chromium.org/2562643003

TBR=noyau@chromium.org,mardini@chromium.org,olivierrobin@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=577659
NOTRY=true

Review-Url: https://codereview.chromium.org/2564293002
Cr-Commit-Position: refs/heads/master@{#437799}

components/reading_list/core/BUILD.gn

@@ -2,22 +2,12 @@
 # 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

@@ -6,12 +6,23 @@
 
 #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() {
-  return BUILDFLAG(ENABLE_READING_LIST);
+  // Reading list is only enabled on iOS.
+#if defined(OS_IOS)
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(kEnableReadingList)) {
+    return true;
+  }
+#endif
+  return false;
 }
 }  // namespace switches
 }  // namespace reading_list

components/reading_list/core/reading_list_switches.h

@@ -7,6 +7,9 @@
 
 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

@@ -234,6 +234,13 @@ 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/ios_chrome_profile_sync_service_factory_unittest.cc

@@ -45,7 +45,6 @@ class IOSChromeProfileSyncServiceFactoryTest : public testing::Test {
     datatypes.push_back(syncer::PASSWORDS);
     datatypes.push_back(syncer::PREFERENCES);
     datatypes.push_back(syncer::PRIORITY_PREFERENCES);
-    datatypes.push_back(syncer::READING_LIST);
     datatypes.push_back(syncer::SESSIONS);
     datatypes.push_back(syncer::PROXY_TABS);
     datatypes.push_back(syncer::TYPED_URLS);