Replace pointers in ComputedStyle::*DataEquivalent functions with refs.

Currently, there are a few *DataEquivalent functions in ComputedStyle
that take a pointer. All these functions assume that the pointers are
not null, so we can simply replace them with references.

BUG=628043

Review-Url: https://codereview.chromium.org/2905793002
Cr-Commit-Position: refs/heads/master@{#474924}
2 files changed