Handle app custom icon via aura::Window property.

extensions/common/manifest_handlers/icons_handler.cc

Index: extensions/common/manifest_handlers/icons_handler.cc
diff --git a/extensions/common/manifest_handlers/icons_handler.cc b/extensions/common/manifest_handlers/icons_handler.cc
index 2825ae917b7dcf672fd4551ffa9d0b5ed79a9467..ba1e50adf1a00c839749f54b7f6da072f5127e98 100644
--- a/extensions/common/manifest_handlers/icons_handler.cc
+++ b/extensions/common/manifest_handlers/icons_handler.cc
@@ -28,8 +28,10 @@ static base::LazyInstance<ExtensionIconSet>::DestructorAtExit g_empty_icon_set =
 
 // static
 const ExtensionIconSet& IconsInfo::GetIcons(const Extension* extension) {
-  IconsInfo* info = static_cast<IconsInfo*>(
-      extension->GetManifestData(keys::kIcons));
+  IconsInfo* info =
+      extension
+          ? static_cast<IconsInfo*>(extension->GetManifestData(keys::kIcons))
+          : nullptr;
   return info ? info->icons : g_empty_icon_set.Get();
 }