Ensure tests have an active task runner

chrome/browser/chromeos/power/power_prefs_unittest.cc

Index: chrome/browser/chromeos/power/power_prefs_unittest.cc
diff --git a/chrome/browser/chromeos/power/power_prefs_unittest.cc b/chrome/browser/chromeos/power/power_prefs_unittest.cc
index 9bf1e9c57dc958c6a8706f6293a27c1fbe849d2f..dbf34eae15db759cdc8193d268dc65aed0b46118 100644
--- a/chrome/browser/chromeos/power/power_prefs_unittest.cc
+++ b/chrome/browser/chromeos/power/power_prefs_unittest.cc
@@ -32,6 +32,7 @@
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
+#include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace chromeos {
@@ -60,6 +61,7 @@ class PowerPrefsTest : public testing::Test {
   bool GetExpectedAllowScreenWakeLocksForProfile(Profile* profile) const;
   bool GetCurrentAllowScreenWakeLocks() const;
 
+  content::TestBrowserThreadBundle thread_bundle_;
   TestingProfileManager profile_manager_;
   PowerPolicyController* power_policy_controller_;     // Not owned.
   scoped_ptr<FakePowerManagerClient> fake_power_manager_client_;