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If the current wallpaper was set by a third party application, we should disable surprise me feature,
otherwise the wallpaper will still be changed periodically.

Also fix the issue that wallpaper picker application can't load the local resource:
chrome://resources/css/text_defaults.css.

BUG=466709
TEST=Manually tested

Review URL: https://codereview.chromium.org/1004263002

Cr-Commit-Position: refs/heads/master@{#320972}