Force calling PostDisplayConfigurationChange() even if earyling out in UpdateDisplays

ash/display/display_manager.cc

Index: ash/display/display_manager.cc
diff --git a/ash/display/display_manager.cc b/ash/display/display_manager.cc
index 29eced4cc03ec6eee89c4e70a04ad674edb7a05b..c61b876e68f36e198acbcf4e40b3654ccf274db7 100644
--- a/ash/display/display_manager.cc
+++ b/ash/display/display_manager.cc
@@ -889,6 +889,14 @@ void DisplayManager::UpdateDisplays(
   // http://crbug.com/155948.
   if (display_changes.empty() && added_display_indices.empty() &&
       removed_displays.empty()) {
+    // When changing from software mirroring mode to sinlge display mode, it
+    // is possible there is no need to update |displays_| and we early out
+    // here. But we still want to run the PostDisplayConfigurationChange()
+    // cause there are some clients need to act on this, e.g.
+    // TouchTransformerController needs to adjust the TouchTransformer when
+    // switching from dual displays to single display.
+    if (delegate_)

[Yufeng Shen (Slow to review), 2014/09/11 16:24:02]

hmmm, DisplayControllerTest catches this that we must pair
PreDisplayConfigurationChange with PostDisplayConfigurationChange.

Should we also call PreDisplayConfigurationChange() here  ? or should we change
the test ?

[oshima, 2014/09/11 17:19:08]

Yes, it has to be paired. You can move the PreDisplay.. below

[Yufeng Shen (Slow to review), 2014/09/11 18:25:49]

Done.

+      delegate_->PostDisplayConfigurationChange();
     return;
   }
   // Clear focus if the display has been removed, but don't clear focus if