Logging accesses to URL-properties of DOM elements, e.g., src.
Logging calls to submit method of Form elements.

This CL allows UMA logging of the following extension activities:
- an extension sets a url property on a DOM element within a page, e.g., 
the extension's content script set src property of an image element.
- an extension's content script calls submit method on a Form element 
within a page. 

BUG=313901,313878

Review URL: https://codereview.chromium.org/55313003

git-svn-id: svn://svn.chromium.org/blink/trunk@161238 bbb929c8-8fbe-4397-9dbb-9b2b20218538