Selecting subfolders on the bookmark bar which have many entries can be quite laggy

[luixxiul]

Test plan

#10301 (comment)

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Describe the issue you encountered: While doing QA for #4879 I noticed that selecting subfolders on the bookmark bar which have many bookmarks can be laggy. It sometimes takes 1 second to open subfolders.

• Platform (Win7, 8, 10? macOS? Linux distro?): Windows 10 32 bit

• Brave Version (revision SHA): 0.13.2 RC3

• Steps to reproduce:

  1. Import a number of bookmarks
  2. Open a folder on bookmark bar which has many entries
  3. Open subfolders by moving the mouse fast

• Actual result: The context menu is selected quite slowly

• Expected result: the subfolders should be selected instantly

• Screenshot if needed:
  

• Any related issues:

[srirambv]

This happens only when a large amount of bookmarks are loaded. With just few bookmarks there is no perf issue

[luixxiul]

@ayumi Is this issue fixed with one of the PRs you recently pushed?

[sjlehn]

Possibly related - on Mac OSX (El Capitan), when selecting a group of bookmarks and moving them to another folder there is considerable lag

[luixxiul]

@NejcZdovc do you think this was fixed with the recent split PR?

[NejcZdovc]

@luixxiul I think it will be fixed with this PR #10301

[luixxiul]

I updated the 1st post on #10301 (comment)

[luixxiul]

Closing for now to check if #10301 (comment) really fixes the issue.