Remove picture->unique() assert.
Remove picture->unique() assert.

Some pictures (namely, empty pictures) may soon not be unique.

An alternative that'd work for now is to draw something into the
recording canvas so the picture in this test isn't empty.

BUG=

Review URL: https://codereview.chromium.org/1138053002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@195185 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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