Reland "CrOS: Enable Hyper-Threading by default if core scheduler is available."

This is a reland of d24c918a

Original change's description:
> CrOS: Enable Hyper-Threading by default if core scheduler is available.
>
> If the kernel supports core scheduling, Hyper-Threading is enabled by
> default. Users, admins and Finch may still override this setting.
>
> BUG=b:152605392
>
> Change-Id: Iffcec33455ec277ec6f79f03908d02015c7d1f6f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2209676
> Reviewed-by: James Cook <jamescook@chromium.org>
> Reviewed-by: Mattias Nissler <mnissler@chromium.org>
> Commit-Queue: Greg Kerr <kerrnel@chromium.org>
> Auto-Submit: Greg Kerr <kerrnel@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#774920}

Bug: b:152605392
Change-Id: I50590824454aa5d33267d0c6783b002c1925fe3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584566Reviewed-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Auto-Submit: Joel Fernandes <joelaf@google.com>
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835773}

chrome/browser/chromeos/scheduler_configuration_manager.cc

@@ -91,8 +91,10 @@ void SchedulerConfigurationManager::OnPrefChange() {
     // Next, if Finch isn't set, see if the command line passed in a default.
     config_name = cmdline_default;
   } else {
-    // If nothing is found, default to conservative.
-    config_name = debugd::scheduler_configuration::kConservativeScheduler;
+    // If nothing is found, default to core isolation scheduling. Note that
+    // only some kernels support core isolation. debugd checks for support and
+    // reverts to conservative if core isolation is unavailable.
+    config_name = debugd::scheduler_configuration::kCoreIsolationScheduler;
   }
 
   // NB: Also send an update when the config gets reset to let the system pick

chrome/browser/chromeos/scheduler_configuration_manager_unittest.cc

@@ -117,7 +117,7 @@ TEST_F(SchedulerConfigurationManagerTest, ConfigChange) {
   manager.AddObserver(this);
 
   task_environment_.RunUntilIdle();
-  EXPECT_EQ(debugd::scheduler_configuration::kConservativeScheduler,
+  EXPECT_EQ(debugd::scheduler_configuration::kCoreIsolationScheduler,
             debug_daemon_client_.scheduler_configuration_name());
   EXPECT_EQ(1u, configuration_set_count_);
 
@@ -144,7 +144,7 @@ TEST_F(SchedulerConfigurationManagerTest, ConfigChange) {
   // Dropping the policy as well reverts to the default configuration.
   local_state_.RemoveManagedPref(prefs::kSchedulerConfiguration);
   task_environment_.RunUntilIdle();
-  EXPECT_EQ(debugd::scheduler_configuration::kConservativeScheduler,
+  EXPECT_EQ(debugd::scheduler_configuration::kCoreIsolationScheduler,
             debug_daemon_client_.scheduler_configuration_name());
   EXPECT_EQ(5u, configuration_set_count_);
 }