Move StyleBackgroundData.cpp to be inline in StyleBackgroundData.h

This patch removes StyleBackgroundData.cpp, and moves all its contents
to be inline in StyleBackgroundData.h

This is prework for generating StyleBackgroundData.

BUG=628043

Review-Url: https://codereview.chromium.org/2860663002
Cr-Commit-Position: refs/heads/master@{#468937}
3 files changed