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Previously it would open the item then immediately minimize it. This caused
user confusion because they tried a double-click and didn't see anything
open on the screen.

BUG=404060
TEST=ash_unittests ShelfViewTest.ClickingTwiceActivatesOnce

Review URL: https://codereview.chromium.org/492963008

Cr-Commit-Position: refs/heads/master@{#291695}