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For offTheSideButton, animation was always enabled regardless of nodeMoved/
nodeRemoved. Enable animation only when it is called from -nodeRemoved:,
decided by 'animate' parameter.

BUG=60628
R=asvitkine@chromium.org

TEST=
1. Launch chrome and add more bookmarks and folders so that chevron is seen.
2. Drag and adjust items so that there is atleast one folder and one or more bookmarks under chevron.
3. Drag a bookmark(within chevron) and drop it under the folder(within chevron) and observe.
4. There should be no poof animation/sound presented to see/hear.

Review URL: https://codereview.chromium.org/599793002

Cr-Commit-Position: refs/heads/master@{#297105}