Add BackgroundModeOptimizer that can restart the browser

chrome/browser/background/background_mode_manager_unittest.cc

Index: chrome/browser/background/background_mode_manager_unittest.cc
diff --git a/chrome/browser/background/background_mode_manager_unittest.cc b/chrome/browser/background/background_mode_manager_unittest.cc
index ab892378bd05139c3e4cb87c507318306583dee0..6da58ea0297cc791a5bba4c131e1650d02ea114c 100644
--- a/chrome/browser/background/background_mode_manager_unittest.cc
+++ b/chrome/browser/background/background_mode_manager_unittest.cc
@@ -261,12 +261,14 @@ class BackgroundModeManagerWithExtensionsTest : public testing::Test {
     // We're getting ready to shutdown the message loop. Clear everything out!
     base::RunLoop().RunUntilIdle();
 
-    test_keep_alive_.reset();
-
     // TestBackgroundModeManager has dependencies on the infrastructure.
     // It should get cleared first.
     manager_.reset();
 
+    // Now that the background manager is destroyed, the test KeepAlive can be
+    // cleared without having |manager_| attempt to perform optimizations.
+    test_keep_alive_.reset();
+
     // The Profile Manager references the Browser Process.
     // The Browser Process references the Notification UI Manager.
     // The Notification UI Manager references the Message Center.