Use ElementTraversal in HTMLTableRowsCollection::rowAfter()

Use ElementTraversal in HTMLTableRowsCollection::rowAfter() instead of
traversing manually. This makes it clearer that we are looking for Elements and
is good for performance as ContainerNode::firstChild() gets called instead of
Node::firstChild().

RoboHornet Pro benchmark is 1.7-1.8% faster with this patch on my Linux desktop.

R=adamk, eseidel

Review URL: https://codereview.chromium.org/163573004

git-svn-id: svn://svn.chromium.org/blink/trunk@167151 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove an unused parameter from HashTable(Const)Iterator constructors.

SSIA. The 'const HashTableType* table' constructor parameter is not
used anyhow at the moment, so can be removed.

Review URL: https://codereview.chromium.org/153003006

git-svn-id: svn://svn.chromium.org/blink/trunk@167152 bbb929c8-8fbe-4397-9dbb-9b2b20218538