Create PaintChunk and begin writing code to build paint chunks.

BUG=537409

Review URL: https://codereview.chromium.org/1379883003

Cr-Commit-Position: refs/heads/master@{#352369}
    OutOfOrderIndexContext(DisplayItems::iterator begin) : nextItemToIndex(begin) { }

    OutOfOrderIndexContext(DisplayItems::iterator begin) : nextItemToIndex(begin) { }
