Move RareNonInheritedData::*DataEquivalent to ComputedStyle.

When we generate RareNonInheritedData, we would no longer generate
helper methods like ReflectionDataEquivalent. These need to be
handwritten in ComputedStyle. This patch moves these helper methods
from RareNonInheritedData to ComputedStyle.

This is preparation for generating RareNonInheritedData.

BUG=628043

Review-Url: https://codereview.chromium.org/2907713002
Cr-Commit-Position: refs/heads/master@{#474958}
4 files changed