https://bugs.webkit.org/show_bug.cgi?id=104882
<rdar://problem/12872298>

Reviewed by Filip Pizlo.

The crash occurs because the strings might be null. Add a check for it, but also try to infer a MIME type
in case the markup does not include a type attribute, but we can find it from the extension in the URL.

* platform/KURL.cpp: Add a new function mimeTypeFromURL() which tries to return the implied MIME type
based on the URL provided. If nothing was found, return a null string.
(WebCore::mimeTypeFromURL): Factored out from FrameLoader::defaultObjectContentType().
* platform/KURL.h:

* loader/FrameLoader.cpp:
(WebCore::FrameLoader::defaultObjectContentType): Refactor to use mimeTypeFromURL().
* plugins/PlugInOriginHash.cpp:
(WebCore::addCaseFoldedCharacters): Add a check for an empty string.
(WebCore::PlugInOriginHash::hash): If the service type is empty, try to infer the MIME type.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@137573 268f45cc-cd09-0410-ab3c-d52691b4dbfc