Make canvas filters use the font size in effect when the filter is set
This snapshots the current font when a new filter is set,
and uses the snapshotted font whenever the filter is rebuilt,
rather than using the current font. The filter is no longer
rebuilt for changes to the current font. This matches Firefox's
behavior.
BUG=
601877
Committed:
https://crrev.com/222eb4b80b8531ca616f78207033427d359c2879
Cr-Commit-Position: refs/heads/master@{#388099}