Centralizes more shared code between ash and mash

ash/test/display_manager_test_api.cc

Index: ash/test/display_manager_test_api.cc
diff --git a/ash/test/display_manager_test_api.cc b/ash/test/display_manager_test_api.cc
index e0bb4db1dfa40454a9add288622fe8719a30b389..18758af85045697738d6d49778ea1d2c8df18a1b 100644
--- a/ash/test/display_manager_test_api.cc
+++ b/ash/test/display_manager_test_api.cc
@@ -95,7 +95,7 @@ void DisplayManagerTestApi::UpdateDisplay(const std::string& display_specs) {
   // previous one for GPU performance reasons. Try to emulate the behavior
   // unless host origins are explicitly set.
   if (!is_host_origin_set) {
-    // Sart from (1,1) so that windows won't overlap with native mouse cursor.
+    // Start from (1,1) so that windows won't overlap with native mouse cursor.
     // See |AshTestBase::SetUp()|.
     int next_y = 1;
     for (DisplayInfoList::iterator iter = display_info_list.begin();