Do not update FileSystemUsageCache if the delta is zero

webkit/fileapi/sandbox_quota_observer.cc

 // 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.
 
 #include "webkit/fileapi/sandbox_quota_observer.h"
 
 #include "base/sequenced_task_runner.h"
 #include "webkit/fileapi/file_system_url.h"
 #include "webkit/fileapi/file_system_usage_cache.h"
 #include "webkit/fileapi/file_system_util.h"
@@ skipping 16 matching lines @@
 void SandboxQuotaObserver::OnStartUpdate(const FileSystemURL& url) {
   DCHECK(SandboxMountPointProvider::CanHandleType(url.type()));
   DCHECK(update_notify_runner_->RunsTasksOnCurrentThread());
   FilePath usage_file_path = GetUsageCachePath(url);
   if (usage_file_path.empty())
     return;
   FileSystemUsageCache::IncrementDirty(usage_file_path);
 }
 
 void SandboxQuotaObserver::OnUpdate(const FileSystemURL& url,
-                                          int64 delta) {
+                                    int64 delta) {
   DCHECK(SandboxMountPointProvider::CanHandleType(url.type()));
   DCHECK(update_notify_runner_->RunsTasksOnCurrentThread());
   FilePath usage_file_path = GetUsageCachePath(url);
   if (usage_file_path.empty())
     return;
-  FileSystemUsageCache::AtomicUpdateUsageByDelta(usage_file_path, delta);
+  if (delta != 0)
+    FileSystemUsageCache::AtomicUpdateUsageByDelta(usage_file_path, delta);
   if (quota_manager_proxy_) {
     quota_manager_proxy_->NotifyStorageModified(
         quota::QuotaClient::kFileSystem,
         url.origin(),
         FileSystemTypeToQuotaStorageType(url.type()),
         delta);
   }
 }
 
 void SandboxQuotaObserver::OnEndUpdate(const FileSystemURL& url) {
@@ skipping 22 matching lines @@
       sandbox_file_util_, url.origin(), url.type(), &error);
   if (error != base::PLATFORM_FILE_OK) {
     LOG(WARNING) << "Could not get usage cache path for: "
                  << url.DebugString();
     return FilePath();
   }
   return path;
 }
 
 }  // namespace fileapi