Add explicit keyword to constructors that take one argument

BUG=None

Review URL: https://chromiumcodereview.appspot.com/22893004

git-svn-id: svn://svn.chromium.org/blink/trunk@156023 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Measure usage for Element methods removed from DOM4

Measure usage for the following Element methods removed from DOM4:
- getAttributeNode()
- getAttributeNodeNS()
- setAttributeNode()
- removeAttributeNode()

This will help us determine if we should deprecate them or if they should
be reintroduced in DOM4.

R=arv
BUG=272098

Review URL: https://chromiumcodereview.appspot.com/22963004

git-svn-id: svn://svn.chromium.org/blink/trunk@156024 bbb929c8-8fbe-4397-9dbb-9b2b20218538