Add imgblur tool to assist BlurMaskFilter debugging

imgblur is intended to establish a ground truth for debugging mask blur issues. It performs a brute force (non-separable) Gaussian blur of the provided image.

The blur code itself is in sk_tools_utils so it can be more easily used programmatically in other places (e.g., blur unit tests).

Review URL: https://codereview.chromium.org/1384203002
4 files changed