[GTK] MHTML files not being loaded due to reported mime type not supported

https://bugs.webkit.org/show_bug.cgi?id=89978

Reviewed by Carlos Garcia Campos.

Source/WebCore:

Make 'message/rfc822' a supported MIME type for MHTML files in GTK.

* loader/MainResourceLoader.cpp:
(WebCore::MainResourceLoader::continueAfterContentPolicy): Add
'message/rfc822' to the list of MIME types to be considered to
avoid them bypasing cross-domain security checks, only for GTK.
* loader/archive/ArchiveFactory.cpp:
(WebCore::archiveMIMETypes): Add 'message/rfc822' to the list of
supported MIME types when MHTML support is enabled in GTK.

LayoutTests:

Move expectations for MHTML tests out of chromium's specific directory.

* mhtml/multi_frames_binary-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/multi_frames_binary-expected.txt.
* mhtml/multi_frames_ie-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/multi_frames_ie-expected.txt.
* mhtml/multi_frames_unmht-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/multi_frames_unmht-expected.txt.
* mhtml/page_with_css_and_js_ie-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/page_with_css_and_js_ie-expected.txt.
* mhtml/page_with_css_and_js_unmht-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/page_with_css_and_js_unmht-expected.txt.
* mhtml/page_with_image_ie-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/page_with_image_ie-expected.txt.
* mhtml/page_with_image_unmht-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/page_with_image_unmht-expected.txt.
* mhtml/simple_page_ie-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/simple_page_ie-expected.txt.
* mhtml/simple_page_unmht-expected.txt: Renamed from LayoutTests/platform/chromium/mhtml/simple_page_unmht-expected.txt.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@123088 268f45cc-cd09-0410-ab3c-d52691b4dbfc