This happens in ports with sandbox extensions disabled, and it's making several tests to crash in debug builds. The SandboxExtension implementation is empty in case of building with sandbox extensions disabled, so that we are actually allocating no extensions at all in NetworkProcessProxy::grantSandboxExtensionsToDatabaseProcessForBlobs(). When the message arrives to database process, we have a list of paths, but an empty list of hanldes which causes the assertion. We can just avoid that message entirely in case of building without sandbox extensions.
Created attachment 284567 [details]
Yup looks good.
Committed r203856: <http://trac.webkit.org/changeset/203856>