Check IsFixed specifically instead of presence of other flags.

LayoutSVGRoot::mapLocalToAncestor has an assert to check that there is
no fixed content in the SVG layout tree. However, it did incorrectly
rely on MapCoordinatesFlags being non-0. Changed the assert to check
for the Fixed flag explicitly instead.

R=mstensho@opera.com
BUG=586478

Review URL: https://codereview.chromium.org/1697543002

Cr-Commit-Position: refs/heads/master@{#375458}
4 files changed