Delay incrementing shields counter until first render

[srirambv]

Test Case

• only update resources blocked after shields is active for the site brave-core#2507 (comment)

Original Issue

Description

Shields starts showing blocked count even before page is loaded in webview

Steps to Reproduce

1. Upgrade to 0.54.3
2. Open a new tab and load a site
3. Before the page is loaded in webview, shields starts showing blocked count in badge even on disabled icon before changing to active icon (see recording below)

Actual result:

Expected result:

Should only show badge when icon is active and not on inactive icon

Reproduces how often:

100%

Brave version (about:brave info)

Brave	0.54.3 Chromium: 70.0.3528.4 (Official Build) dev (64-bit)
Revision	1911f781145b803e04f2d0b5b1a0146ae69fcbdc-refs/branch-heads/3528@{#9}
OS	Windows

Reproducible on current release:

No

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
• Is the issue reproducible on the latest version of Chrome?

Additional Information

cc: @brave/legacy_qa @bbondy @petemill

[LaurenWags]

Reproduced on macOS with 0.55.3

[tildelowengrimm]

Updated title. Cezar, if this isn't implementable with the APIs you currently have access to, I'll move it to the backend pile.