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.

TBR=pdr@google.com

Review URL: https://codereview.chromium.org/112133005

git-svn-id: svn://svn.chromium.org/blink/trunk@163677 bbb929c8-8fbe-4397-9dbb-9b2b20218538