Create a baseline RenderBlock::lineHeight() performance

This test calls RenderBlock::lineHeight() ~425,000 times on each run.
I hope to remove the caching of RenderStyle::computedLineHeight() by
|m_lineHeight| in RenderBlock so this will baseline will ensure it
doesn't regress performance.

Review URL: https://codereview.chromium.org/256593009

git-svn-id: svn://svn.chromium.org/blink/trunk@175356 bbb929c8-8fbe-4397-9dbb-9b2b20218538