Have htmlediting create functions take a Document reference in argument

Have htmlediting create functions take a Document reference in argument instead
of a pointer since they require the document to be non-null. Most of the
callers already have a Document reference so this change avoids having to
convert references into pointers at call sites.

This patch is a prequirement to have HTMLElements take a Document reference
in argument.

BUG=281400

Review URL: https://chromiumcodereview.appspot.com/23548010

git-svn-id: svn://svn.chromium.org/blink/trunk@157092 bbb929c8-8fbe-4397-9dbb-9b2b20218538