function loadJiraUrlElements() {
    return new Promise(function(resolve, reject) {
        chrome.storage.local.get({companyName: '', jiraBaseUrl: ''}, function(items) {
            resolve(items.companyName + items.jiraBaseUrl);
         })
    });
}

// And caller function changes to 
function populateUrlFieldsWithUrlElements(){
    loadJiraUrlElements().then(function(value) {
        companyInput.value = value;
    })
}