Fill the canvas with black background before painting wallpaper

ash/desktop_background/desktop_background_view.cc

Index: ash/desktop_background/desktop_background_view.cc
diff --git a/ash/desktop_background/desktop_background_view.cc b/ash/desktop_background/desktop_background_view.cc
index 04311087b32f677f6f7683bda9398d8ab094c045..8753409f3d2b7e7e2c62c8b032214c832df501e5 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -138,8 +138,11 @@ void DesktopBackgroundView::OnPaint(gfx::Canvas* canvas) {
   gfx::ImageSkia wallpaper = controller->GetWallpaper();
   WallpaperLayout wallpaper_layout = controller->GetWallpaperLayout();
 
+  // Wallpapers with png format could be partially transparent.
+  // Reset the canvas before rendering wallpaper.

[xdai1, 2016/05/19 23:27:55]

Might be better to say "Fill the canvas with black background to make it opaque
before painting wallpaper"?

[xiaoyinh(OOO Sep 11-29), 2016/05/20 00:06:12]

Done.

+  canvas->FillRect(GetLocalBounds(), SK_ColorBLACK);
+

[xdai1, 2016/05/19 23:27:55]

Move this part after if(wallpaper.isNull())...

[xiaoyinh(OOO Sep 11-29), 2016/05/20 00:06:11]

Discussed with xdai1@, this will remain as is.

   if (wallpaper.isNull()) {

[xdai1, 2016/05/19 23:27:55]

No brace please

[xiaoyinh(OOO Sep 11-29), 2016/05/20 00:06:12]

Done.

-    canvas->FillRect(GetLocalBounds(), SK_ColorBLACK);
     return;
   }