Text::textRendererIsNeeded should not use NodeRenderingContext

textRendererIsNeeded should be using the DOM based NodeRenderingTraversal
to correctly traverse to rendered siblings since renderer()->previousSibling()
or nextSibling() could be anonymous content. This also removes the last usage
of NodeRenderingContext outside render tree creation paving the way to
renaming it to something like RenderTreeConstructor or merging it into
Element and Text.

Review URL: https://codereview.chromium.org/120773005

git-svn-id: svn://svn.chromium.org/blink/trunk@164435 bbb929c8-8fbe-4397-9dbb-9b2b20218538