Call GenerateSafeFilename() from GetSuggestedFilename().

      GetSuggestedFilename() would then become the only function that needs to be called to generate downloaded filenames.

BUG=78085
TEST=net_unittests --gtest_filter=*Generate*FileName


Review URL: http://codereview.chromium.org/7607013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97581 0039d316-1c4b-4281-b951-d872f2087c98