Tweak css3 weight score, prevent ties.

The old code could produce ties and didn't make much logical sense.
Now the range between 400 and 500 prefers heavier weights up to 500,
then lower weights, then the least weight above 500.

Change-Id: I4e80f43c039d795efc49a7329c5c64f9da0fd9b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/231957
Reviewed-by: Julia Lavrova <jlavrova@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
2 files changed