As a user I’d like to programmatically alter the appearance of the browser, thus complementing the static theme definition in the manifest. I’d like a single chrome.theme.update(propertyBag) function to be exposed to my WebExtension background scripts. I’d like the property-bag to be a simple object which may only contain properties that are defined in the schema as well.
Example:
```js
chrome.theme.update({
  colors: {
    background_tab: [255, 170, 255]
  }
});
```

Example uses of this API would be a background script which fetches data from weather.com and shows specific background images that fit the current weather type, or a background script checks the time of year and shows specific background images that fit the current meteorological season.