Enable features API for content shell and webview

content/shell/browser/shell_browser_main_parts.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/shell/browser/shell_browser_main_parts.h"
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "components/devtools_http_handler/devtools_http_handler.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/common/content_switches.h"
@@ skipping 106 matching lines @@
 void ShellBrowserMainParts::PreEarlyInitialization() {
 #if !defined(OS_CHROMEOS) && defined(USE_AURA) && defined(OS_LINUX)
   ui::InitializeInputMethodForTesting();
 #endif
 #if defined(OS_ANDROID)
   net::NetworkChangeNotifier::SetFactory(
       new net::NetworkChangeNotifierFactoryAndroid());
 #endif
 }
 
+int ShellBrowserMainParts::PreCreateThreads() {
+    const base::CommandLine* command_line =

[Alexei Svitkine (slow), 2016/03/18 15:03:42]

Indent is wrong.

[Changwan Ryu, 2016/03/23 09:47:36]

Done.

+        base::CommandLine::ForCurrentProcess();
+    scoped_ptr<base::FeatureList> feature_list(new base::FeatureList);
+    feature_list->InitializeFromCommandLine(
+        command_line->GetSwitchValueASCII(switches::kEnableFeatures),
+        command_line->GetSwitchValueASCII(switches::kDisableFeatures));
+
+    base::FeatureList::SetInstance(std::move(feature_list));

[Alexei Svitkine (slow), 2016/03/18 15:03:42]

So this fails because an instance was already registered.

See this CL for how I initially made content shell initialize its FeatureList:

https://codereview.chromium.org/1409933007

The issue is that setting up the instance must only be done once. Right now,
this is done in Chrome code or in FeatureList::InitializeInstance() by content -
which is a no-op if Chrome code already initialized it.

You probably want to expand FeatureList::InitializeInstance() implementation -
with maybe passing the two flags to it.

[Changwan Ryu, 2016/03/23 09:47:36]

Please check crbug.com/596021 for the different approaches I took.
I could not find a perfect solution for this, but instead chose the one that
improves the situation. WDYT?

+    return 0;
+}
+
 void ShellBrowserMainParts::InitializeBrowserContexts() {
   set_browser_context(new ShellBrowserContext(false, net_log_.get()));
   set_off_the_record_browser_context(
       new ShellBrowserContext(true, net_log_.get()));
 }
 
 void ShellBrowserMainParts::InitializeMessageLoopContext() {
   Shell::CreateNewWindow(browser_context_.get(),
                          GetStartupURL(),
                          NULL,
@@ skipping 43 matching lines @@
   device::BluetoothAdapterFactory::Shutdown();
   bluez::BluezDBusManager::Shutdown();
   chromeos::DBusThreadManager::Shutdown();
 #elif defined(OS_LINUX)
   device::BluetoothAdapterFactory::Shutdown();
   bluez::DBusBluezManagerWrapperLinux::Shutdown();
 #endif
 }
 
 }  // namespace