Add more details to showLineTree() output

Sample of the new output:
    InlineFlowBox       0x397ffa898130          RenderInline 0x397ffa840170 {pos=30,13 size=212.271,15} baseline=24/20


R=ojan@chromium.org
BUG=

Review URL: https://codereview.chromium.org/215583003

git-svn-id: svn://svn.chromium.org/blink/trunk@170229 bbb929c8-8fbe-4397-9dbb-9b2b20218538