Attempt to clean up requiresLayoutToDetermineWidth to be more clear

This code is brittle, and definitely wrong in some cases
but hopefully this is more clear now.

We need to find a path to making this more maintainable.  Clearly
this win is worth this complexity, we just need to figure out
how to not have more bad regressions from this.

BUG=247470
R=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/25048006

git-svn-id: svn://svn.chromium.org/blink/trunk@158551 bbb929c8-8fbe-4397-9dbb-9b2b20218538