Make wallpaper picker manifest and thumbnails available when offline.

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 ebdf1a326e4e694d733b0272d6d7d9e67c10d946..ee3014b1485c48b11d06d0db4b5d58c369a19f7e 100644
--- a/chrome/common/extensions/api/wallpaper_private.json
+++ b/chrome/common/extensions/api/wallpaper_private.json
@@ -87,6 +87,57 @@
         "description": "Restores all previously minimized windows.",
         "nodoc": "true",
         "parameters": []
+      },
+      {
+        "name": "getThumbnail",
+        "type": "function",
+        "description": "Gets thumbnail of wallpaper from thumbnail directory.",
+        "nodoc": "true",
+        "parameters": [
+          {
+            "type": "string",
+            "name": "url",
+            "description": "Wallpaper url."
+          },
+          {
+            "type": "function",
+            "name": "callback",
+            "description": "Function called upon completion.",
+            "parameters": [
+              {
+                "type": "binary",
+                "name": "data",
+                "optional": true,
+                "description": "The binary data of loaded thumbnail."
+              }
+            ]
+          }
+        ]
+      },
+      {
+        "name": "saveThumbnail",
+        "type": "function",
+        "description": "Saves thumbnail to thumbnail directory.",
+        "nodoc": "true",
+        "parameters": [
+          {
+            "type": "string",
+            "name": "url",
+            "description": "Wallpaper url."
+          },
+          {
+            "type": "binary",
+            "name": "data",
+            "description": "The binary data of downloaded thumbnail."
+          },
+          {
+            "type": "function",
+            "name": "callback",
+            "description": "Function called upon completion.",
+            "parameters": [],
+            "optional": true
+          }
+        ]
       }
     ]
   }