Consistently use ElementTraversal API when looking for an Element

Consistently use ElementTraversal API when looking for an Element. This often
results in simpler code by getting rid of explicit isElementNode() checks. It
makes it clear we are only interested in Elements and in some cases, allows the
compiler to use faster Element/ContainerNode methods instead of generic Node
ones.

R=adamk, eseidel

Review URL: https://codereview.chromium.org/171663005

git-svn-id: svn://svn.chromium.org/blink/trunk@167462 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Implement TrueType kerning support for HarfBuzz text path.

BUG=41990

Review URL: https://codereview.chromium.org/69513002

git-svn-id: svn://svn.chromium.org/blink/trunk@167463 bbb929c8-8fbe-4397-9dbb-9b2b20218538