IPFS onboarding does not validate postmessage origin

[diracdeltas]

see details at https://github.com/brave/brave-core/security/code-scanning/44?query=ref%3Arefs%2Fheads%2Fmaster

[diracdeltas]

Also as part of this, these other issues should be addressed: https://bravesoftware.slack.com/archives/C7VLGSR55/p1645560425184459

[stephendonner]

Quick (and important) enough change to verify on all platforms -> QA/Test-All-Platforms.

[stephendonner]

Is this code shared with Android's IPFS/gateway support, and should be checked there, too? @spylogsster @diracdeltas

[stephendonner]

Verified PASSED using

Brave	1.37.84 Chromium: 99.0.4844.51 (Official Build) beta (x86_64)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	macOS Version 11.6.3 (Build 20G415)

Steps:

Case 1: Use a Brave local IPFS node

1. install 1.37.84
2. launch Brave
3. load ipns://ipfs.io
4. click on Use a Brave local IPFS node
5. wait for installation

example	example

Confirmed it loaded ipns://ipfs.io

Case 2: Use a public gateway

1. install 1.37.84
2. launch Brave
3. load ipns://ipfs.io
4. click on Use a public gateway

Confirm it loaded https://ipfs-io.ipns.dweb.link/ via public gateway

example	example

---

Verified PASSED using

Brave	1.37.84 Chromium: 99.0.4844.51 (Official Build) beta (64-bit)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	Windows 10 Version 21H2 (Build 19044.1566)

Steps:

Case 1: Use a Brave local IPFS node

1. install 1.37.84
2. launch Brave
3. load ipns://ipfs.io
4. click on Use a Brave local IPFS node
5. wait for installation

example	example

Confirmed it loaded ipns://ipfs.io

Case 2: Use a public gateway

1. install 1.37.84
2. launch Brave
3. load ipns://ipfs.io
4. click on Use a public gateway

Confirm it loaded https://ipfs-io.ipns.dweb.link/ via public gateway

example	example

---

Verification passed on

Brave	1.37.101 Chromium: 99.0.4844.83 (Official Build) beta (64-bit)
Revision	b11086e62d7c1a44b0942ac5568d22a425c7ae35-refs/branch-heads/4844_74@{#5}
OS	Ubuntu 20 LTS

Verified the above test plan

Case 1: Use a Brave local IPFS node

Case 2: Use a public gateway