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Now golden screenshots are kept in Google Storage. To download them automatically, a hook should be added to .gclient. Specifying directories for golden screenshots and artifacts is optional now. There is also a python script that should be run to update screenshots in Google Storage after using update mode.

BUG=395653

Review URL: https://codereview.chromium.org/639283004

Cr-Commit-Position: refs/heads/master@{#299109}