Add use counter for <svg>

This patch adds a use counter for the SVGSVGElement. This will not
over count SVG, as we just record usecounter information once per page,
not per element on the page.

NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/24000002

git-svn-id: svn://svn.chromium.org/blink/trunk@157434 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Introduce Promise mapping to the IDL generator

Since Promise will be implemented in V8-side in the
future, we add the following special conversion rules to the IDL code
generator like DOMString -> const String&, Promise -> ScriptPromise.

BUG=266700

Review URL: https://chromiumcodereview.appspot.com/23479016

git-svn-id: svn://svn.chromium.org/blink/trunk@157435 bbb929c8-8fbe-4397-9dbb-9b2b20218538