Revert 245509 "net: Use FileStream asynchronously from UploadFil..."

This caused XP Tests (2) net_unittests
NextProto/HttpNetworkTransactionTest.UploadFileSmallerThanLength/0, /1, /2,
/3, /4, and UploadDataStreamTest.FileSmallerThanLength to time out.

http://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%282%29/builds/32723/

> net: Use FileStream asynchronously from UploadFileElementReader
> 
> InitInternal() and ReadInternal() were used to share the same implementation with UploadFileElementReaderSync.
> There is no need to maintain them since UploadFileElementReaderSync is gone.
> Abandon these unneeded functions and use FileStream in an asynchronous way.
> 
> BUG=294797
> TEST=net_unittests
> 
> Review URL: https://codereview.chromium.org/139253002

TBR=hashimoto@chromium.org

Review URL: https://codereview.chromium.org/141843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245529 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245529