FastTextAutosizing: apply inflation to parent RenderBlock.

This patch boosts the font size of both the parent block and children
in FastTextAutosizer::inflate. Previously, the parent block would not
get inflated which caused surprising line-height bugs where text would
overlap other text on subsequent lines.

This patch adds a test that verifies that the inflated font size
is observable via javascript. Before this patch, the parent block
did not get autosized so this test would fail. This test trivially
passes with the existing autosizer.

This is a reland of r163677 after fixing a UAF due to caching style()
before layout, laying out, and then using the cached pointer to style
that is now stale.

TBR=pdr@google.com

Review URL: https://codereview.chromium.org/115373004

git-svn-id: svn://svn.chromium.org/blink/trunk@163904 bbb929c8-8fbe-4397-9dbb-9b2b20218538