Disable surprise me automatically if the current wallpaper was set by a third party application.

chrome/browser/chromeos/extensions/wallpaper_api.cc

 // Copyright 2013 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.
 
 #include "chrome/browser/chromeos/extensions/wallpaper_api.h"
 
 #include <string>
 #include <vector>
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "base/files/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/worker_pool.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/extensions/extension_constants.h"
 #include "chrome/common/pref_names.h"
 #include "components/user_manager/user.h"
 #include "components/user_manager/user_manager.h"
 #include "components/wallpaper/wallpaper_layout.h"
+#include "extensions/browser/event_router.h"
 #include "net/base/load_flags.h"
 #include "net/http/http_status_code.h"
 #include "net/url_request/url_fetcher.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
 using base::BinaryValue;
 using content::BrowserThread;
 
 typedef base::Callback<void(bool success, const std::string&)> FetchCallback;
@@ skipping 78 matching lines @@
     GURL wallpaper_url(*params_->details.url);
     if (wallpaper_url.is_valid()) {
       g_wallpaper_fetcher.Get().FetchWallpaper(
           wallpaper_url,
           base::Bind(&WallpaperSetWallpaperFunction::OnWallpaperFetched, this));
     } else {
       SetError("URL is invalid.");
       SendResponse(false);
     }
   }
+
+  Profile* profile = Profile::FromBrowserContext(browser_context());
+  extensions::EventRouter* event_router = extensions::EventRouter::Get(profile);
+  scoped_ptr<base::ListValue> event_args(new base::ListValue());
+  scoped_ptr<extensions::Event> event(new extensions::Event(
+      extensions::api::wallpaper::OnWallpaperChangedBy3rdParty::kEventName,
+      event_args.Pass()));
+  event_router->DispatchEventToExtension(extension_misc::kWallpaperManagerId,
+                                         event.Pass());

[bshe, 2015/03/16 14:02:40]

We should send the event only after we know for sure that the new wallpaper
request success. So move the new code to OnWallpaperDecoded is better.

   return true;
 }
 
 void WallpaperSetWallpaperFunction::OnWallpaperDecoded(
     const gfx::ImageSkia& image) {
   chromeos::WallpaperManager* wallpaper_manager =
       chromeos::WallpaperManager::Get();
   base::FilePath thumbnail_path = wallpaper_manager->GetCustomWallpaperPath(
       wallpaper::kThumbnailWallpaperSubDir, user_id_hash_,
       params_->details.filename);
@@ skipping 76 matching lines @@
     const std::string& response) {
   if (success) {
     params_->details.data.reset(
         new std::vector<char>(response.begin(), response.end()));
     StartDecode(*params_->details.data);
   } else {
     SetError(response);
     SendResponse(false);
   }
 }