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This CL switches Tab Search to use the WebUIBubbleManager and updates
WebUIBubbleManager to handle UMA metrics / extensions APIs.

This CL also removes the now redundant TabSearchBubbleView and
WebBubbleDialogView code.

Bug: 1099917
Change-Id: I808de88af774f91539c9610f066317f155252037
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2514077Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#824018}