Remove the enable_task_manager build flag and define.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index fea7361f58f3c58b12f5f97b3ba5973f26cf1a95..6255e298a6bee352812e82e41c6b9fe7497fc162 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -3611,6 +3611,13 @@ test("unit_tests") {
       "../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.
@@ -4168,17 +4175,6 @@ test("unit_tests") {
     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",