Refine the UseCounter for Document.charset

The DocumentCharset counter is very high, around 4.5%:
http://www.chromestatus.com/metrics/feature/timeline/popularity/127

Measure the setter separately, since it doesn't make much sense and
getting rid of it would make charset a simple alias for characterSet.

Add a separate counter for defaultCharset, which is likely used less.

Note that Document.characterSet is the only attribute in the DOM spec:
http://dom.spec.whatwg.org/#document

Review URL: https://codereview.chromium.org/291823009

git-svn-id: svn://svn.chromium.org/blink/trunk@174738 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use Document::renderView over Document::renderer

This patch switches callers of Document::renderer() to
Document::renderView() which removes a branch. This patch also adds
"void renderer()" to Document to prevent future users from using
renderer() when the faster renderView() is available.

No new tests as there should be no observable change in behavior.

Review URL: https://codereview.chromium.org/294203009

git-svn-id: svn://svn.chromium.org/blink/trunk@174739 bbb929c8-8fbe-4397-9dbb-9b2b20218538