For blocked URLs, we should do 200 status code instead of redirects

[bbondy]

Description

We currently redirect to empty data URLs (or empty image data URLs for images).
We should instead be responding with 200 status code because data URLs can cause CSP violations.

I believe this will help with general webcompat no a large scale.

See also:
https://chromium.googlesource.com/chromium/src/+/master/net/docs/life-of-a-url-request.md

Test plan

See #2554 (comment)

[mrzealot]

Just mentioning this here as well: like #2931 shows, there can be problems with not blocking, too, if the script thinks that it actually managed to load something that we blocked. Possibly these are rarer than the problems solved by not blocking, I don't have numbers, just an FYI.

[iefremov]

@mrzealot Yeah, that makes sense. We are not going to quickly push this change to stable, I think we would rather treat this as an experiment.

[srirambv]

Moving issue to 0.62.x based on brave/brave-core#1377 set milestone. @iefremov please add QA/Yes or QA/No labels accordingly

[iefremov]

@srirambv thanks for pinging me, added QA/Yes

[btlechowski]

@iefremov Could you include a test plan in brave/brave-core#1377?

I have no idea how to test this one.

[iefremov]

@btlechowski

1. Open Devtools
2. Open any website with lots of ads, e.g. https://www.foxnews.com/
   3a. Before this change, in a DevTools console one can see a lot of entries like Access to XMLHttpRequest at 'data:text/plain,'
   3b. After this change, these entries should vanish.
3. There are also no entries like 'data:text/plain,' on a Network tab
4. Ads are blocked as expected

[btlechowski]

Thanks @iefremov !

Verification passed on

Brave	0.62.10 Chromium: 73.0.3683.39 (Official Build) dev (64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Windows 7 Service Pack 1 Build 7601.24312

Used test plan from #2554 (comment)
Checked several sites.

Verification passed on

Brave	0.62.26 Chromium: 73.0.3683.75 (Official Build) beta (64-bit)
Revision	909ee014fcea6828f9a610e6716145bc0b3ebf4a-refs/branch-heads/3683@{#803}
OS	Linux

• Verified the test plan from For blocked URLs, we should do 200 status code instead of redirects #2554 (comment)
  Verified few sites like nytimes, Timesofindia, theverge.com and foxnews
  

Verified passed with

Brave	0.62.31 Chromium: 73.0.3683.75 (Official Build) beta(64-bit)
Revision	909ee014fcea6828f9a610e6716145bc0b3ebf4a-refs/branch-heads/3683@{#803}
OS	Mac OS X

• Verified the test plan from For blocked URLs, we should do 200 status code instead of redirects #2554 (comment)
• Verified few sites like nytimes, foxnews, cnn