Every URL navigation takes 1000+ ms in updateSiteFavicon (With 10K bookmarks)

[ayumi]

Test plan

#9279 (comment)

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

• Describe the issue you encountered:
  Navigating to URLs and clicking links is very slow with 10K bookmarks.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  MacOS

• Brave Version (revision SHA):
  e14a9db

• Steps to reproduce:

  1. Instrument siteUtil.updateSiteFavicon() to measure its runtime.
  2. Load 10K bookmarks.
  3. Go to https://github.com/brave/browser-laptop and see how long updateSiteFavicon takes.
  4. Click the H1 link "browser-laptop" to navigate to the same page and see how long updateSiteFavicon takes.

• Actual result:
  First navigation takes 1000 ms.
  Clicking the link to itself takes 1000 * 2 ms.

• Expected result:
  < 100 ms

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes; with 10K bookmarks

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

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:

• Any related issues:
  Refreshing / navigating away from large pages is very slow #7162