[Desktop] Favicon caching

[fmarier]

https://github.com/brave/internal/issues/716

[kjozwiak]

Verification PASSED on macOS 10.15.6 x64 using the following build:

Brave | 1.15.55 Chromium: 85.0.4183.102 (Official Build) dev (64-bit)
-- | --
Revision | ffe848af6a5df4fa127e2929331116b7f9f1cb30-refs/branch-heads/4183@{#1770}
OS | macOS Version 10.15.6 (Build 19G73)

• Verified via https://github.com/brave/internal/issues/716#issuecomment-694490747.

Verification passed on

Brave	1.15.55 Chromium: 85.0.4183.102 (Official Build) dev (64-bit)
Revision	ffe848af6a5df4fa127e2929331116b7f9f1cb30-refs/branch-heads/4183@{#1770}
OS	Ubuntu 18.04 LTS

• Verified via https://github.com/brave/internal/issues/716#issuecomment-694490747.

---

Verification passed on

Brave | 1.15.65 Chromium: 86.0.4240.55 (Official Build) dev (64-bit)
-- | --
Revision | a6d625ef6f7fe8ea0675f1cf759155a05ee1be40-refs/branch-heads/4240@{#953}
OS | Windows 10 OS Version 1903 (Build 18362.1016)

• Verified via https://github.com/brave/internal/issues/716#issuecomment-694490747.