Revert of Make SelectionPopupController.ShowPastePopup only be triggered by Blink (patchset #3 id:40001 of https://codereview.chromium.org/2721813002/ )

Reason for revert:
Caused flakiness (crbug.com/697934)

Original issue's description:
> Make SelectionPopupController.ShowPastePopup only be triggered by Blink
>
>
> This patch is progress towards the goal of having Blink triggering all
> of clank's SelectActionMode context menus. In particular this patch
> has Blink trigger the menu when an insertion handle is tapped or
> dragged.
>
> BUG=627234
>
> Review-Url: https://codereview.chromium.org/2721813002
> Cr-Commit-Position: refs/heads/master@{#454203}
> Committed: https://chromium.googlesource.com/chromium/src/+/f88569b6a113509e7e7245ca297221701d07d4a3

TBR=aelias@chromium.org,boliu@chromium.org,jinsukkim@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=627234

Review-Url: https://codereview.chromium.org/2727203003
Cr-Commit-Position: refs/heads/master@{#454355}
7 files changed