Do not monitor system power state during unit tests.

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index d2bc9de87448a7298feedddac32b15c09734a4d7..5b955eb5f697d8a04be456f4374c98c4aeb30e52 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -265,6 +265,11 @@ int BrowserMain(const MainFunctionParams& parameters) {
 
   // Initialize the SystemMonitor
   base::SystemMonitor::Start();
+#if defined(OS_WIN)
+  // We want to monitor system power state to adjust our high resolution
+  // timer settings. But it's necessary only on Windows.
+  base::Time::StartSystemMonitorObserver();
+#endif  // defined(OS_WIN)
 
   // Initialize statistical testing infrastructure.
   FieldTrialList field_trial;