[Suggestions Component] Add missing NULL check to ImageManager::OnImageFetched().

components/suggestions/image_manager.cc

 // Copyright 2014 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 "components/suggestions/image_manager.h"
 
 #include "base/bind.h"
 #include "components/suggestions/image_encoder.h"
 #include "components/suggestions/image_fetcher.h"
 
@@ skipping 48 matching lines @@
     // Once database is initialized, it will serve pending requests from either
     // cache or network.
     QueueCacheRequest(url, image_url, callback);
     return;
   }
 
   ServeFromCacheOrNetwork(url, image_url, callback);
 }
 
 void ImageManager::OnImageFetched(const GURL& url, const SkBitmap* bitmap) {
-  SaveImage(url, *bitmap);
+  if (bitmap)  // |bitmap| can be nullptr if image fetch was unsuccessful.
+    SaveImage(url, *bitmap);
 }
 
 bool ImageManager::GetImageURL(const GURL& url, GURL* image_url) {
+  DCHECK(image_url);
   std::map<GURL, GURL>::iterator it = image_url_map_.find(url);
   if (it == image_url_map_.end()) return false;  // Not found.
   *image_url = it->second;
   return true;
 }
 
 void ImageManager::QueueCacheRequest(
     const GURL& url, const GURL& image_url,
     base::Callback<void(const GURL&, const SkBitmap*)> callback) {
   // To be served when the database has loaded.
@@ skipping 114 matching lines @@
        it != pending_cache_requests_.end(); ++it) {
     const ImageCacheRequest& request = it->second;
     for (CallbackVector::const_iterator callback_it = request.callbacks.begin();
          callback_it != request.callbacks.end(); ++callback_it) {
       ServeFromCacheOrNetwork(request.url, request.image_url, *callback_it);
     }
   }
 }
 
 }  // namespace suggestions