Implement range reading for NetworkReaderProxy.

The feature is not yet actually used, but will be used for range reading
of DriveFileStreamReader.

BUG=127129
TEST=Ran unit_tests

Review URL: https://chromiumcodereview.appspot.com/14493008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@196636 0039d316-1c4b-4281-b951-d872f2087c98
void GetFileContentByPath(
    const DriveFileStreamReader::DriveFileSystemGetter& file_system_getter,
    const base::FilePath& drive_file_path,
    const GetFileContentInitializedCallback& initialized_callback,
    const google_apis::GetContentCallback& get_content_callback,
    const FileOperationCallback& completion_callback) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));

  BrowserThread::PostTask(
      BrowserThread::UI,
      FROM_HERE,
      base::Bind(&GetFileContentByPathOnUIThread,
                 file_system_getter,
                 drive_file_path,
                 google_apis::CreateRelayCallback(initialized_callback),
                 google_apis::CreateRelayCallback(get_content_callback),
                 google_apis::CreateRelayCallback(completion_callback)));
}

void GetFileContentByPath(
    const DriveFileStreamReader::DriveFileSystemGetter& file_system_getter,
    const base::FilePath& drive_file_path,
    const GetFileContentInitializedCallback& initialized_callback,
    const google_apis::GetContentCallback& get_content_callback,
    const FileOperationCallback& completion_callback) {
  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));

  BrowserThread::PostTask(
      BrowserThread::UI,
      FROM_HERE,
      base::Bind(&GetFileContentByPathOnUIThread,
                 file_system_getter,
                 drive_file_path,
                 google_apis::CreateRelayCallback(initialized_callback),
                 google_apis::CreateRelayCallback(get_content_callback),
                 google_apis::CreateRelayCallback(completion_callback)));
}
