Add some error messages for setting wallpaper failures on Chrome(c++) side.

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * WallpaperManager constructor.
  *
  * WallpaperManager objects encapsulate the functionality of the wallpaper
  * manager extension.
  *
@@ skipping 175 matching lines @@
       this.wallpaperRequest_.open('GET', wallpaperURL, true);
       this.wallpaperRequest_.responseType = 'arraybuffer';
       this.wallpaperRequest_.send(null);
       this.butterBar_.setRequest(this.wallpaperRequest_);
       var self = this;
       this.wallpaperRequest_.addEventListener('load', function(e) {
         if (self.wallpaperRequest_.status === 200) {
           var image = self.wallpaperRequest_.response;
           chrome.wallpaperPrivate.setWallpaper(image,
                                                selectedItem.layout,
-                                               wallpaperURL);
+                                               wallpaperURL,
+                                               self.onFinished_.bind(self));
           self.currentWallpaper_ = wallpaperURL;
         } else {
           self.butterBar_.showError_(str('downloadFailed'));
         }
         self.wallpaperRequest_ = null;
       });
     }
     this.setWallpaperAttribution_(selectedItem);
   };
 
@@ skipping 101 matching lines @@
 
   /**
    * Refreshes the custom wallpaper with the current selected layout.
    * @param {ArrayBuffer} customWallpaper The raw wallpaper file data.
    */
   WallpaperManager.prototype.refreshWallpaper_ = function(customWallpaper) {
     var setWallpaperLayout = $('set-wallpaper-layout');
     var layout =
         setWallpaperLayout.options[setWallpaperLayout.selectedIndex].value;
     chrome.wallpaperPrivate.setCustomWallpaper(customWallpaper,
-                                               layout);
+                                               layout,
+                                               this.onFinished_.bind(this));
     this.currentWallpaper_ = 'CUSTOM';
   };
 
   /**
+   * Sets wallpaper finished. Displays error message in butter bar if any.
+   */
+  WallpaperManager.prototype.onFinished_ = function() {
+    if (chrome.runtime.lastError != undefined)
+      this.butterBar_.showError_(chrome.runtime.lastError.message);
+    else
+      this.butterBar_.hide_();
+  };
+
+  /**
    * Handles the layout setting change of custom wallpaper.
    */
   WallpaperManager.prototype.onWallpaperLayoutChanged_ = function() {
     if (this.customWallpaperData_)
       this.refreshWallpaper_(this.customWallpaperData_);
   };
 
   /**
    * Generates a thumbnail of user selected image file.
    * @param {Object} file The file user selected from file manager.
@@ skipping 51 matching lines @@
             selectedItem = wallpaperInfo;
           }
         }
       }
       this.wallpaperGrid_.dataModel = wallpapersDataModel;
       this.wallpaperGrid_.selectedItem = selectedItem;
     }
   };
 
 })();