Uplift to 0.71.x: Rewards button icon pre-opt-in gets correct scaling (#3830)

[petemill]

Rewards button icon pre-opt-in gets correct scaling

Original #3830

Sets the scale of the image compared to the size we want to display it, so that the underlying Draw function can work out if the image needs to be re-sized or not. Previously this was only happening (coincidentally) when the display was not using a scaling factor of 1 since this would not match the default scaling factor of the gfx::Image. Resize is done here: https://github.com/chromium/chromium/blob/0aa1854a269704ce0dd45641cfb9d440666e54bc/chrome/browser/ui/extensions/icon_with_badge_image_source.cc#L147-L148

Fix: brave/brave-browser#6663

This should be uplifted to wherever #3698 is uplifted to (currently 0.71.x).

[kjozwiak]

Restrating macOS as npm run test -- brave_unit_tests Release --output brave_unit_tests.xml failed due to the following error as per https://ci.brave.com/job/brave-browser-build-pr/job/fix-6663-bat-icon-scale-71/1/execution/node/711/log/:

07:20:36  [252/257] CXX obj/brave/test/brave_browser_tests/brave_content_browser_client_browsertest.o
07:22:13  Sending interrupt signal to process
07:22:28  ninja: error: remove(brave_browser_tests.dSYM): Directory not empty
07:22:28  ninja: build stopped: interrupted by user.
07:22:28  ninja: error: remove(brave_browser_tests.dSYM): Directory not empty
07:22:28  script returned exit code 143

[petemill]

@kjozwiak CI is successful now

[kjozwiak]

Uplift into 0.71.x approved after deliberating with @brave/uplift-approvers. Both CI/Jenkins and CI/Travis passed without any issues.

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