Remove the enable_task_manager build flag and define.

chrome/test/BUILD.gn

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
@@ skipping 3593 matching lines @@
       "../browser/search/instant_unittest_base.h",
       "../browser/search/search_unittest.cc",
 
       # GCMDriverAndroid is not yet implemented.
       "../browser/services/gcm/gcm_profile_service_unittest.cc",
       "../browser/sessions/persistent_tab_restore_service_unittest.cc",
       "../browser/speech/extension_api/extension_manifests_tts_unittest.cc",
       "../browser/speech/tts_controller_unittest.cc",
       "../browser/sync/sessions/sessions_sync_manager_unittest.cc",
       "../browser/sync/sync_ui_util_unittest.cc",  # Sync setup uses native ui.
+      "../browser/task_manager/providers/browser_process_task_unittest.cc",
+      "../browser/task_manager/providers/child_process_task_unittest.cc",
+      "../browser/task_manager/sampling/shared_sampler_unittest_win.cc",
+      "../browser/task_manager/sampling/task_manager_impl_unittest.cc",
+      "../browser/task_manager/task_manager_observer_unittest.cc",
+      "../browser/task_manager/test_task_manager.cc",
+      "../browser/task_manager/test_task_manager.h",
       "../browser/translate/translate_manager_render_view_host_unittest.cc",
 
       # The autofill popup is implemented in mostly native code on Android.
       "../browser/ui/autofill/autofill_popup_controller_unittest.cc",
       "../browser/ui/bookmarks/bookmark_context_menu_controller_unittest.cc",
       "../browser/ui/bookmarks/bookmark_unittest.cc",
       "../browser/ui/browser_close_unittest.cc",
       "../browser/ui/browser_command_controller_unittest.cc",
       "../browser/ui/browser_instant_controller_unittest.cc",
       "../browser/ui/browser_unittest.cc",
@@ skipping 537 matching lines @@
       "//chrome/browser/ui/startup/startup_tab_provider_unittest.cc",
     ]
   }
   if (use_gio) {
     deps += [ "//build/linux/libgio" ]
   }
   if (!is_chromeos && !use_ozone && is_linux) {
     deps += [ "//chrome/browser/ui/libgtkui" ]
   }
 
-  if (enable_task_manager) {
-    sources += [
-      "../browser/task_manager/providers/browser_process_task_unittest.cc",
-      "../browser/task_manager/providers/child_process_task_unittest.cc",
-      "../browser/task_manager/sampling/shared_sampler_unittest_win.cc",
-      "../browser/task_manager/sampling/task_manager_impl_unittest.cc",
-      "../browser/task_manager/task_manager_observer_unittest.cc",
-      "../browser/task_manager/test_task_manager.cc",
-      "../browser/task_manager/test_task_manager.h",
-    ]
-  }
   if (enable_mdns) {
     sources += [
       "../browser/local_discovery/local_domain_resolver_unittest.cc",
       "../browser/local_discovery/service_discovery_client_unittest.cc",
       "../browser/printing/cloud_print/privet_device_lister_unittest.cc",
       "../browser/printing/cloud_print/privet_local_printer_lister_unittest.cc",
     ]
   }
   if (enable_service_discovery) {
     sources += [
@@ skipping 933 matching lines @@
 }
 
 if (is_win) {
   loadable_module("conflicts_dll") {
     testonly = true
     sources = [
       "conflicts/conflicts_dll.cc",
     ]
   }
 }