Cleanup in task management and threading in FilebrowseHandler.
Cleanup in task management and threading in FilebrowseHandler.

CreateNewFolder should be on file thread.
Delete TaskProxy on ui thread where applicable.
Use scoped_refptr for TaskProxy lifetime management.
Deprecate use of current_task_ as much as possible by using function args instead.
Fix a bug where certain actions cannot be performed running Cros chrome on linux due to over-zealous security. This includes downloads, deletes and copies.
Filter out .crdownload files.
Fix lint errors.

BUG=chromium-os:8130
TEST=Create a folder using advanced filesystem Save As dialog in debug mode, threading asserts should no longer fire. Download a large non-dangerous file, .crdownload file should no longer appear.

Review URL: http://codereview.chromium.org/6246118

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@74524 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser