Don't use hasAttribute in SVGFilterPrimitiveStandardAttributes

Use isSpecified() to query for existance in setStandardAttributes. This
avoids triggering unnecessary attribute synchronizations.

While here, drop the "double precondition" checking since the only caller
of this function checks this already.

BUG=235256

Review-Url: https://codereview.chromium.org/2026343002
Cr-Commit-Position: refs/heads/master@{#397202}
3 files changed