Improve FileSystemUsageCache performance
FileSystemUsageCache calls open/read/write/close for each request to manage usage cache and dirty flag.
This may hurt performance of consecutive file operation.
This patch changes it to keep file handles open for a while to avoid open/close overhead.
BUG=181425
Review URL: https://chromiumcodereview.appspot.com/12734004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@188082 0039d316-1c4b-4281-b951-d872f2087c98
10 files changed
