background.js

var QueueWorker = function() {
  this.queues = [];
  this.tabId = null;
  this.loaded = false;
  this.push = function(details) {
    this.queues.push(details);
    this.notify();
  }

  this.notify = function() {
    if(this.tabId === null || !this.loaded) {
      return;
    }
    while (this.queues.length != 0) {
      var details = this.queues.shift();
      chrome.tabs.sendMessage(this.tabId, details, function(response){
        if (chrome.runtime.lastError) {
          console.log("chrome.runtime.lastError" + chrome.runtime.lastError.message);
        }
      });
    }
  }
}
var worker = new QueueWorker();

function check(tabId, changeInfo, tab) {
  if (tab.url.indexOf('backlog.jp') > 0
      || tab.url.indexOf('backlogtool.com') > 0
      || tab.url.indexOf('backlog.com') > 0) {
    chrome.pageAction.show(tabId);
    if (tab.status === 'complete') {
      worker.tabId = tabId;
      worker.notify();
    }
  }
};
chrome.tabs.onUpdated.addListener(check);
chrome.runtime.onMessage.addListener(function(request, sender, callback) {
  if(request.message === "unload") {
    worker.tabId = null;
    worker.loaded = false;
  } else if(request.message === "loaded") {
    worker.loaded = true;
    worker.notify();
  }
});
chrome.webRequest.onHeadersReceived.addListener(function (details) {
    if(details.statusCode !== 302) {
      worker.push(details);
    }
  }, {
    urls: ["https://*.backlog.jp/*", "https://*.backlog.com/*", "https://*.backlogtool.com/*"],
    types: ["main_frame", "xmlhttprequest"]
  }, ["responseHeaders"]
);