[TabManager] Enable tab discarding by default.

chrome/browser/memory/tab_manager_browsertest.cc

 // Copyright (c) 2012 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 "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 15 matching lines @@
 #include "content/public/test/test_utils.h"
 #include "url/gurl.h"
 
 using content::OpenURLParams;
 
 #if defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX)
 
 namespace memory {
 
 class TabManagerTest : public InProcessBrowserTest {
- public:
-  // Tab discarding is enabled by default on CrOS. On other platforms, force it
-  // by turning on the corresponding experiment as some tests assume this
-  // behavior it turned on.
-  void SetUpCommandLine(base::CommandLine* command_line) override {
-#if !defined(OS_LINUX)
-    command_line->AppendSwitchASCII(switches::kEnableFeatures,
-                                    features::kAutomaticTabDiscarding.name);
-#endif
-  }
 };
 
 IN_PROC_BROWSER_TEST_F(TabManagerTest, TabManagerBasics) {
   using content::WindowedNotificationObserver;
   TabManager* tab_manager = g_browser_process->GetTabManager();
   EXPECT_FALSE(tab_manager->recent_tab_discard());
 
   // Disable the protection of recent tabs.
   tab_manager->set_minimum_protection_time_for_tests(
       base::TimeDelta::FromMinutes(0));
@@ skipping 385 matching lines @@
   tab_manager->SetTabAutoDiscardableState(tsm->GetWebContentsAt(0), true);
 
   // Now it should be able to discard the tab.
   EXPECT_TRUE(tab_manager->DiscardTabImpl());
   EXPECT_TRUE(tab_manager->IsTabDiscarded(tsm->GetWebContentsAt(0)));
 }
 
 }  // namespace memory
 
 #endif  // OS_WIN || OS_MAXOSX || OS_LINUX