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While setting up the scrollbar layer if the properties of the scrollbar
layer didn't change, then avoid setting update_draw_properties.
Scrollbar needs animation if any of the scrollbar properties changed.
In the same way set update_draw_properties if scrollbar properties
are changed.

Review URL: https://codereview.chromium.org/595913002

Cr-Commit-Position: refs/heads/master@{#296193}