WebDataSource::isClientRedirect should mean what it says.

It previously returned DocumentLoader::replacesCurrentHistoryItem(), because
its sole caller in RenderViewImpl expected it. Now it should return
DocumentLoader::isClientrRedirect(), so RenderViewImpl can use it and simplify
its logic.

BUG=261374

Review URL: https://chromiumcodereview.appspot.com/20000004

git-svn-id: svn://svn.chromium.org/blink/trunk@154776 bbb929c8-8fbe-4397-9dbb-9b2b20218538