[fsp] Check for modification time in the file stream reader.

According to the FileStreamReader interface, we have to check the modification
time if it is the same as the expected one.

Note, that we can provide a better file integration mechanisms within providing
extensions.

TEST=unit_tests: *FileSystemProviderFileStreamReader*Modif*
BUG=248427

Review URL: https://codereview.chromium.org/366073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@281247 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed