Sync Metamask Storage across multiple Chrome instances

[tmashuang]

Look into chrome.storage API.

Issues with:
Sending Txs through different chrome instances
Diluting the importance of Seed Phrase

[step21]

Also combine it with Firefox sync, please. https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/storage/sync Also already mentioned here: #1459 (though this issue here is someday, while the other is soon)

[Gudahtt]

Closing this in favour of #6540, which is about the more general problem rather than Chrome sync specifically.

Nevermind, #6540 includes syncing between mobile and extension as well, which this does not. I'll re-open this.