Inline images can be specified in two different ways -- explicitly with a
Content-Disposition of "inline" or implicitly with no Content-Disposition.
We correctly handled the former. For the later, we now default to an "inline"
disposition if one was not specified. This is acceptable per RFC 822 which
states:
Content-Disposition is an optional header field. In its absence,
the MUA may use whatever presentation method it deems suitable.
Additionally, if the disposition is not specified by the server, we need to
look at the Content-Type header for the file name.
bug 2824698
Change-Id: I146f7a67197b4e737e5f82a3d570e0f74e23fa35
39121c758d