Hook up custom wallpaper code path to new wallpaper picker.

chrome/common/extensions/api/wallpaper_private.json

Index: chrome/common/extensions/api/wallpaper_private.json
diff --git a/chrome/common/extensions/api/wallpaper_private.json b/chrome/common/extensions/api/wallpaper_private.json
index 8de1464c26343d199a6874f9eb39b1d7b6479938..c4efae6d2895f43eb23bcf3baa4277063e244d10 100644
--- a/chrome/common/extensions/api/wallpaper_private.json
+++ b/chrome/common/extensions/api/wallpaper_private.json
@@ -46,6 +46,23 @@
             "name": "url"
           }
         ]
+      },
+      {
+        "name": "setCustomWallpaper",
+        "type": "function",
+        "description": "Sets wallpaper to the image from local file with specified layout",
+        "nodoc": "true",
+        "parameters": [
+          {
+            "type": "binary",
+            "name": "wallpaper"
+          },
+          {
+            "type": "string",
+            "name": "layout",
+            "enum": [ "STRETCH", "CENTER", "CENTER_CROPPED"]
+          }
+        ]
       }
     ]
   }