check shield setting before blocking WebGL shader API

[pes10k]

Resolves brave/brave-browser#12310
Resolves brave/brave-browser#12366
Resolves brave/brave-browser#12448

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Verified that these changes build without errors on
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint, npm run gn_check)
• Ran git rebase master (if needed).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Requested a security/privacy review as needed.
• Added appropriate QA labels (QA/Yes or QA/No) to the associated issue
• Added appropriate release note labels (release-notes/include or release-notes/exclude) to the associated issue
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

Test Plan:

Go to Google Maps and see if you can scroll smoothly in and out with the scroll wheel or similar (in other words, make sure the issues in brave/brave-browser#12310 does not still happen)

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[pilgrim-brave]

CI failures are unrelated:

00:54:07      RewardsContributionBrowserTest.TipConnectedPublisherVerified (../../brave/components/brave_rewards/browser/test/rewards_contribution_browsertest.cc:580)
00:54:07      RewardsPromotionBrowserTest.PromotionRemovedFromEndpoint (../../brave/components/brave_rewards/browser/test/rewards_promotion_browsertest.cc:228)

so merging

[kjozwiak]

Verification PASSED on macOS 10.15.7 x64 using the following build:

Brave | 1.19.2 Chromium: 87.0.4280.49 (Official Build) nightly (x86_64)
-- | --
Revision | f77f85899646b42a1d3c8ff36794e00becab9171-refs/branch-heads/4280@{#1115}
OS | macOS Version 10.15.7 (Build 19H2)

Case #1 via brave/brave-browser#12366:

Visited https://webglreport.com and ensured that float/int precision: appears as highp/highp as per the following:

Case #2 via brave/brave-browser#12448:

Visited https://netmap.vodafone.de/cokart-client/index.html?lang=de&app=cokart_4x and ensured the map was loading as per the following:

Case #3 via brave/brave-browser#12310:

Ensured that zooming in/out via the mouse/trackpad wasn't as sensitive as before.