Angular fetches template HTML files outside of the browser's normal parsing flow. As a result, URLs in template files are interpreted relative to the root application, when the components defined by the template files are inserted into the DOM. This change enables a template author to prefix URLs with the string $baseUrl, which will be replaced with the relative base path of the template file.
So for an example template loaded from /component/foo/template.html:
<img src="$baseUrl/logo.png" />
becomes:
<img src="/component/foo/logo.png" />
Addresses #2384.