Chrome Extension API: chrome.tabs.captureVisibleTab on Background Page to Content Script

Chrome Extension API: chrome.tabs.captureVisibleTab on Background Page to
Content Script

My overall goal was to take a screenshot via the background page using:
http://developer.chrome.com/extensions/tabs.html#method-captureVisibleTab
and pass it to the content script so I can use the page's HTML DOM to
analyze the screenshot and cut it up the way I would like.
However, I can't seem to pass the dataUrl back to the content script with
Message Passing:
http://developer.chrome.com/extensions/messaging.html
I tried JSON.stringify() but to no avail.
This works perfectly fine:
background.js
chrome.runtime.onMessage.addListener(
function(request, sender, sendResponse) {
sendResponse({imgSrc:'hello'});
}
);
I switch the code to this and nothing gets through:
background.js
chrome.runtime.onMessage.addListener(
function(request, sender, sendResponse) {
chrome.tabs.captureVisibleTab(
null,
{},
function(dataUrl)
{
sendResponse({imgSrc:dataUrl});
}
)
}
);
My only proof that the background page is actually taking a screenshot is
that I can do
chrome.tabs.captureVisibleTab(null,{},function(dataUrl){console.log(dataUrl);});
and I see
"data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAA....etc..."
logged in background.html, which is valid
My question is: HOW CAN I SEND THIS STUPID URL TO THE CONTENT SCRIPT?!?!
I would prefer not to do all the logic on the background page which can't
control anything on the actual visible page because it seems so
unnecessary and ridiculous.