Preserve original line endings on File Save

TEST=
  1. Go to example.com
  2. Tools > Save page as...
  3. Save to "Example Domain.mhtml"
  4. Open it in a tab -- page displays properly.
  5. Open "Example Domain.mhtml" in Text
  6. Change the `<h1>` text to "foo"
  7. Switch to the tab in Chrome. Hit Reload.
  8. The page displays "foo"

BUG=http://crbug.com/369874