Regression(r164102): CSS Selector queries on duplicate ids match non-descendant elements

After r164102, CSS Selector queries on duplicate ids match non-descendant
elements. It returns ALL elements with the given identifier, without checking
that these are descendant of the scope Element.

This CL adds the missing scope check.

BUG=331692
TEST=fast/dom/SelectorAPI/duplicate-id-scope.html
R=esprehn, abarth

Review URL: https://codereview.chromium.org/93863004

git-svn-id: svn://svn.chromium.org/blink/trunk@164484 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Rename NodeRenderingContext to RenderTreeBuilder

NodeRenderingContext is only used during render tree construction so
rename it for that purpose. I also removed previousRenderer() since
nothing uses it and made all the methods private except the two
create methods which are used by Element and Text.

Finally I added a bunch of ASSERTs to the constructor which will
ensure that this is only used in the right places.

Review URL: https://codereview.chromium.org/102123014

git-svn-id: svn://svn.chromium.org/blink/trunk@164485 bbb929c8-8fbe-4397-9dbb-9b2b20218538