Block autoplay by default but allow the user to change it

[bbondy]

I think the popup window is too much on each site and can get in the way of browsing. I find it almost as annoying as the autoplay itself. I think just the URL bar thing like widevine is enough.

Putting in 1.x backlog, but I'd love a patch.

[rebron]

Autoplay without sound is on by default in chrome/firefox/safari. We should match that behavior for autoplay without sound.

Example: https://www.simplehuman.com and https://www.tesla.com/models (scroll to mid-page car driving video - range section)

[bbondy]

We'll do the sound only task in the context of #1088

[btlechowski]

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Brave	0.55.10 Chromium: 70.0.3538.22 (Official Build) beta (64-bit)
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OS	Windows 7

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Brave	0.55.10 Chromium: 70.0.3538.22 (Official Build) beta(64-bit)
Revision	ac9418ba9c3bd7f6baaffa0b055dfe147e0f8364-refs/branch-heads/3538@{#468}
OS	Mac OS X

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Brave	0.55.11 Chromium: 70.0.3538.35 (Official Build) beta (64-bit)
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OS	Linux