268 Ports Associated with Chrome
Asynchronous DNS on Chrome, read more about it at The Chromium Projects
Long story short: Chrome uses native Windows synchronous DNS resolutions by default, which means it has to wait for every resolution successively, regardless of how many tabs are concurrently loading, which will add a noticeable lag to their loading depending on the order they resolve new hosts. A proposed solution was to make this component asynchronous, for this Chrome needed to bypass the native DNS component of Windows, add one of its own, and thus open a few more UDP ports when needed.
That behaviour, in the top question, is due to the component being in development stage and thus will appear so, have many connections, being unrestricted and a resource waster. This was happening only if the user manually changed a flag in Chrome to activate this feature, usually reserved for developers or contributors. See "Obsolete answer" for an explanation on how to access on older versions of Chrome.
For the newer versions of Chrome, I can say for v43, this behaviour has been fixed, and now it uses fewer UDP ports depending on the number of unknown hosts it needs to resolve, otherwise it will use cached resolutions and have fewer opened ports.
As far as I can tell, current versions of Chrome don't have a flag for enabling it, it does exist and can be enabled through a switch on chrome.exe. By default, it's disabled.
Edit Chrome's shortcuts and add --enable-async-dns after the chrome.exe" target, separate them through a space. In Windows 7, for a pinned shortcut, right click the pin, in the tile menu right click the Google Chrome shortcut above the Unpin this program... option and access its properties, edit the Target there.
To find out if Asynchronous DNS is enabled, access chrome://net-internals/#dns and there should be a listing called Internal DNS client enabled: true or false
Obsolete answer (option exists in older versions, around 27):
Enter this in the address bar of Google Chrome:
chrome://flags/
Scroll down the list and make sure "Built-in Asynchronous DNS" is Disabled.