Google Chrome Extension Not Working As Expected - google-chrome-extension

Question

So I'm trying my hand at a google chrome extension which in theory should be extremely straight forward. I know there are tons of stack queries and I've tried a few, I've even copied and pasted direct solutions for testing and I have been unsuccessful. So here is the project. When a page loads, check the html content, and change the icon programmatically.
This is my content.js
chrome.tabs.onUpdated.addListener( function (tabId, changeInfo, tab) {
if (changeInfo.status == 'complete' && tab.active) {
var markup = document.documentElement.innerHTML;
var m = markup.indexOf("candy");
if (m > -1) {
chrome.browserAction.setIcon({path: "check.png"});
} else {
chrome.browserAction.setIcon({path: "cross.png"});
}
}
})
This is my manifest.json
{
"manifest_version": 2,
"name": "Tag Analyzer Plugin",
"description": "Check if tag exist on page",
"version": "1.0",
"browser_action": {
"default_icon": "cross.png"
},
"content_scripts": [
{
"matches": [
"<all_urls>"
],
"js": ["content.js"]
}
],
"permissions": ["<all_urls>"]
}
Right now I'm running this item as a content script because as a content script I can use the logic
var markup = document.documentElement.innerHTML;
var m = markup.indexOf("candy");
if (m > -1) {} else {}
However as a content script the chrome API stuff doesn't work. When I run this script as a background script the script works, except that
var markup = document.documentElement.innerHTML;
doesn't return the pages html, it returns the injected script html.
I've read this stack which was informative as to what the difference was and I've read and tested many stacks like here this, without much success. So obviously i'm missing something and doing something wrong. Thank in advanced for any help.
UPDATES:
So I've made some modifications, but it's still not working, though I think that it's closer to working.
As per the comments below I am now using a content script and background script. No errors are being thrown, however the background script isn't doesn't anything.
content.js
var markup = document.documentElement.innerHTML;
var m = markup.indexOf("candy");
if (m > -1) {
chrome.runtime.sendMessage({"found" : true});
} else {
chrome.runtime.sendMessage({"found": false});
}
background.js
chrome.runtime.onMessage.addListener(
function(request, sender, sendResponse) {
if request.found {
alert("HERE");
chrome.browserAction.setIcon({
path: "check.png",
tabId: sender.tab.id
});
} else {
alert("HERE2");
chrome.browserAction.setIcon({
path: "cross.png",
tabId: sender.tab.id
});
}
});
manifest.json
{
"manifest_version": 2,
"name": "Tag Analyzer Plugin",
"description": "find tag on page",
"version": "1.0",
"browser_action": {
"default_icon": "cross.png"
},
"background": {
"scripts": ["background.js"],
"persistent": false
},
"content_scripts": [
{
"matches": [
"<all_urls>"
],
"js": ["content.js"]
}
],
"permissions": ["<all_urls>"]
}
I've added some alerts on the background.js to see if it was being trigger and nothing, not does the icon change.