Get the default device scale factor from monitor

ash/monitor/multi_monitor_manager_unittest.cc

Index: ash/monitor/multi_monitor_manager_unittest.cc
diff --git a/ash/monitor/multi_monitor_manager_unittest.cc b/ash/monitor/multi_monitor_manager_unittest.cc
index 60ea1ac8153f3f751a45797af3bf8631de706b7f..9be73b1ecc102626a3cc6cf6a6ddc27ed9e8569a 100644
--- a/ash/monitor/multi_monitor_manager_unittest.cc
+++ b/ash/monitor/multi_monitor_manager_unittest.cc
@@ -31,7 +31,8 @@ vector<Monitor> CreateMonitorsFromString(
   base::SplitString(specs, ',', &parts);
   for (vector<string>::const_iterator iter = parts.begin();
        iter != parts.end(); ++iter) {
-    monitors.push_back(aura::MonitorManager::CreateMonitorFromSpec(*iter));
+    monitors.push_back(
+        aura::MonitorManager::CreateMonitorFromSpec(1.0f, *iter));
   }
   return monitors;
 }