Bookmarks manager: no scrollbar, can no longer drag-and-drop into folders

[capouch]

Test plan

#9199 (comment)

Original issue description

• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  I can no longer drag and drop saved bookmarks into folders, and the bookmarks manager window does not have a scrollbar--some bookmarks are invisible off the bottom of the screen.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Linux Slackware 14-current

• Brave Version (revision SHA):
  0.15.305 2186b3f

• Steps to reproduce:

  1. Bookmarks -> Bookmarks
  2. Tap saved bookmark and drag into folder
  3. Nothing happens

• Actual result:
  All saved bookmarks remain on bookmarks toolbar, which does not scroll

• Expected result:
  Like until recently, bookmarks are moved into folders

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  Yes

• Can this issue be consistently reproduced?
  Yes

** Worked fine until one of the recent releases in the last week or so.

[bsclifton]

cc: @cezaraugusto