src/vs/platform/configuration/common/configurationModels.ts/Configuration/compareAndUpdateDefaultConfiguration
class Configuration:	compareAndUpdateDefaultConfiguration(defaults: ConfigurationModel, keys: string[]): IConfigurationChange {
		const overrides: [string, string[]][] = keys
			.filter(key => OVERRIDE_PROPERTY_PATTERN.test(key))
			.map(key => {
				const overrideIdentifier = overrideIdentifierFromKey(key);
				const fromKeys = this._defaultConfiguration.getKeysForOverrideIdentifier(overrideIdentifier);
				const toKeys = defaults.getKeysForOverrideIdentifier(overrideIdentifier);
				const keys = [
					...toKeys.filter(key => fromKeys.indexOf(key) === -1),
					...fromKeys.filter(key => toKeys.indexOf(key) === -1),
					...fromKeys.filter(key => !objects.equals(this._defaultConfiguration.override(overrideIdentifier).getValue(key), defaults.override(overrideIdentifier).getValue(key)))
				];
				return [overrideIdentifier, keys];
			});
		this.updateDefaultConfiguration(defaults);
		return { keys, overrides };
	}