Don't explicitly initialize LayoutUnit to 0.
The default LayoutUnit() constructor sets it to 0. Explicitly passing 0 means
that LayoutUnit::setValue() will be involved, which performs (in this case:
very pointless) saturation checks.
Committed:
https://crrev.com/3e0d01bb6765429ee3d2347337e1c8a490bd1165
Cr-Commit-Position: refs/heads/master@{#396223}