Always populate the node map in SVGFilterBuilder if one exists

Since the node map is essentially a "reverse DAG" we cannot have holes
in it, so always add the FilterEffects even we cannot provide the
LayoutObject -> FilterEffect mapping (like in the case of a non-attached
element.)

BUG=541593, 533457

Review URL: https://codereview.chromium.org/1393633007

Cr-Commit-Position: refs/heads/master@{#353620}
3 files changed