Remove faulty assertion in LayoutSVGResourceContainer::registerResource

When notifying pending elements we don't know what resource type the
registration is for, so it's entirely plausible that the resource type
is one that a possible client isn't really interested in (like a 'mask'
ending up pointing to a <filter>, like in this particular case.)

BUG=687985

Review-Url: https://codereview.chromium.org/2680683003
Cr-Commit-Position: refs/heads/master@{#448688}
3 files changed