support function as parameter in custom paint input arguments.

Example: paint(myPaintFunc, Calc(1px + 2px), rgb(10, 10, 10)) can be parsed and used.

BUG=672647

Review-Url: https://codereview.chromium.org/2698083003
Cr-Commit-Position: refs/heads/master@{#453767}
4 files changed