Minimize black screen during the boot with multi displays

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
index 84da8b0d635c4c345ab0546492e3ef67b9a44722..8ef8311e6a6505367f36449cfba1f2829f580c6d 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -132,7 +132,7 @@ class DesktopBackgroundController::WallpaperLoader
 
 DesktopBackgroundController::DesktopBackgroundController()
     : locked_(false),
-      desktop_background_mode_(BACKGROUND_SOLID_COLOR),
+      desktop_background_mode_(BACKGROUND_NONE),
       background_color_(kTransparentColor),
       weak_ptr_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
 }
@@ -180,6 +180,10 @@ int DesktopBackgroundController::GetWallpaperIDR() const {
 
 void DesktopBackgroundController::OnRootWindowAdded(
     aura::RootWindow* root_window) {
+  // The background hasn't set yet.

[bshe, 2013/01/25 21:46:34]

Just curiosity, if we skip the installation here, when do we install the
background widget on the second screen? Would this function get called twice?

[oshima, 2013/01/25 21:51:49]

This can be called during the boot, before the background is set
by startup process. The background will set after all root windows are created.

[Daniel Erat, 2013/01/26 15:52:30]

nit: s/hasn't set/hasn't been set/

[oshima, 2013/01/26 23:10:42]

Done.

+  if (desktop_background_mode_ == BACKGROUND_NONE)
+    return;
+
   // Handle resolution change for "built-in" images.
   if (BACKGROUND_IMAGE == desktop_background_mode_ &&
       current_wallpaper_.get()) {
@@ -347,9 +351,9 @@ void DesktopBackgroundController::InstallDesktopController(
       component = new internal::DesktopBackgroundWidgetController(layer);
       break;
     }
-    default: {

[oshima, 2013/01/25 21:22:52]

removing default as desktop_background_mode_ is enum.

+    case BACKGROUND_NONE:

[bshe, 2013/01/25 21:46:34]

nit: Could you wrap the following with {} to be consistent?

[oshima, 2013/01/25 21:51:49]

{} is necessary when you create variables, which doesn't apply here. I don't
think we need {} just for consistency,
but I can be convinced either way. Dan, WDTY?

[Daniel Erat, 2013/01/26 15:52:30]

I'd vote for leaving out the curly brackets.

       NOTREACHED();
-    }
+      return;
   }
   // Ensure we're only observing the root window once. Don't rely on a window
   // property check as those can be cleared by tests resetting the background.