Advertise additional mime types in Linux desktop file

The new MIME types are
* application/pdf
* The types listed in firefox.desktop

R=thestig

Fixes: 1046912
Change-Id: I23e314694a08677f13cee8c1399ae68b58f1aab7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2031865
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736994}

chrome/installer/linux/common/desktop.template

@@ -111,7 +111,7 @@ Terminal=false
 Icon=@@PACKAGE@@
 Type=Application
 Categories=Network;WebBrowser;
-MimeType=text/html;text/xml;application/xhtml_xml;image/webp;x-scheme-handler/http;x-scheme-handler/https;x-scheme-handler/ftp;
+MimeType=application/pdf;application/rdf+xml;application/rss+xml;application/xhtml+xml;application/xhtml_xml;application/xml;image/gif;image/jpeg;image/png;image/webp;text/html;text/xml;x-scheme-handler/ftp;x-scheme-handler/http;x-scheme-handler/https;
 Actions=new-window;new-private-window;
 
 [Desktop Action new-window]