Revert r207560 and r207566 to reland r207511.

ash/ash_switches.cc

Index: ash/ash_switches.cc
diff --git a/ash/ash_switches.cc b/ash/ash_switches.cc
index cc6445553184e63d404f578051c803981d5408e0..2e1ef810af85c5e264988415678ac04a741101ee 100644
--- a/ash/ash_switches.cc
+++ b/ash/ash_switches.cc
@@ -29,6 +29,17 @@ const char kAshCopyHostBackgroundAtBoot[] = "ash-copy-host-background-at-boot";
 // Enable keyboard shortcuts useful for debugging.
 const char kAshDebugShortcuts[] = "ash-debug-shortcuts";
 
+// Default wallpaper to use in guest mode (as paths to trusted,
+// non-user-writable JPEG files).
+const char kAshDefaultGuestWallpaperLarge[] =
+    "ash-default-guest-wallpaper-large";
+const char kAshDefaultGuestWallpaperSmall[] =
+    "ash-default-guest-wallpaper-small";
+
+// Default wallpaper to use (as paths to trusted, non-user-writable JPEG files).
+const char kAshDefaultWallpaperLarge[] = "ash-default-wallpaper-large";
+const char kAshDefaultWallpaperSmall[] = "ash-default-wallpaper-small";
+
 // Disable auto window maximization logic.
 const char kAshDisableAutoMaximizing[] = "ash-disable-auto-maximizing";