Skip lots of display checks in adjustRenderStyle when possible

1.5% of the time in the peacekeeper benchmark (and 2% of the recalcStyle
time) is spent inside adjustRenderStyle. This patch is the start of
trying to make adjustRenderStyle do less work in the common cases.

This patch moves the logic for adjusting the style based on the display
property out into a function and adds an early return for when the
element is display: block and is not floating since none of the other
sections of the function are needed then.

Review URL: https://codereview.chromium.org/202283003

git-svn-id: svn://svn.chromium.org/blink/trunk@169425 bbb929c8-8fbe-4397-9dbb-9b2b20218538