Enable chromium translation engine

[atuchin-m]

1. Add new base::Feature and flag (i.e. BraveInternalTranslate)
2. Enable both buildflags enable_brave_translate_go and enable_brave_translate_extension
3. Rewrite buidlflags-related code in the way that the new flag makes sense (not compile-time buidlflags).
4. Make already installed translate extension to have a priority over internal translation
5. Check that network requests are properly redirected to Brave backend (see)

for QA:

1. check that a already installed google translate extension works well
2. check that there is now conflicts between internal translation and extension-based

[stephendonner]

@atuchin-m 👋 ! Would you mind expounding on the QA section quite a bit? Step-by-step instructions would be fantastic; thanks!

[atuchin-m]

Hi @stephendonner.
The feature is complicated that's why there are no simple steps to check everything.

(most important) without the feature UseBraveTranslateGo:

1. Check that nothing has changed (against current stable): user can see a bubble asking to install the Google Translate extension, the bubble works well, and user can translate sites using the extension. The internal translation is not available.

with the feature UseBraveTranslateGo/flag:

1. (most important) If a user has enabled Google Translate extension, it has a priority (the internal translation is not available, the extension works well)
2. If the extension is disabled, a user can a native translate bubble.
3. The number of languages from/to translate must be equal to this set.
4. When the backend is ready, the bubble should work: you can actually translate the page. Right now, you can test the feature only on staging with the google translate endpoint and some switches to disable security checks. After the backend will ready we need to test this scenario again.
   Command-line for staging:
   "C:\Program Files\BraveSoftware\Brave-Browser-Nightly\Application\brave.exe" --enable-features=UseBraveTranslateGo --use-google-translate-endpoint --translate-security-origin=https://translate.bravesoftware.com/ --translate-script-url=https://translate.bravesoftware.com/static/element.js --disable-web-security --disable-site-isolation-trials --user-data-dir=<some_test_temp_dir> (please replace <some_test_temp_dir> to something)

About the specs:

1. I don't know if we have a spec for the old bubble that suggests extension installation.
2. For the internal translation we have only a mini spec from @moritzhaller which compares several solutions. But the feature reused chromium engine/logic.
   @rebron could you help us?

Note:

1. the internal translate engine takes into account this setting (see a screenshot). If you disabled it previously then the engine should be disabled.
2. If you pass --translate-security-origin=/--translate-script-url= the warning bubble is ok. Otherwise, you shouldn't see it.

P.S.: also you can ask questions in slack #machine-translation

[LaurenWags]

QA/Blocked pending more information on internal translations, etc. cc @rebron @brave/legacy_qa

[stephendonner]

Spot-checked on both

Brave	1.33.95 Chromium: 96.0.4664.45 (Official Build) dev (64-bit)
Revision	76e4c1bb2ab4671b8beba3444e61c0f17584b2fc-refs/branch-heads/4664@{#947}
OS	Linux

and

Brave	1.33.95 Chromium: 96.0.4664.45 (Official Build) dev (x86_64)
Revision	76e4c1bb2ab4671b8beba3444e61c0f17584b2fc-refs/branch-heads/4664@{#947}
OS	macOS Version 11.6.1 (Build 20G224)

Confirmed:

• Install Google Translate... dialog appears on various non-English websites (and doesn't when not needed)
• Install button installs Google Translate
• Don't ask again persists across tabs
• Cancel in the dialog cancels without applying changes
• Translate this page works
• am not prompted by our internal engine, which remains behind the feature flag

[LaurenWags]

awesome, thanks @stephendonner 👍🏻

you good with the checks from #18593 (comment) @rebron? I think they cover what we discussed 😄