Move computeInlinePreferredLogicalWidths to RenderBlockLineLayout

Only RenderBlockFlows have inline children, and furthermore, code
for dealing with inline children lives in RenderBlockLineLayout.
This patch moves the code out of RenderBlock. It also adds some
FIXMEs to break the mammoth function up.

Ultimately, RenderBlock shouldn't be aware of its inline child
mode at all, which will clean up this code path.

I also tried to remove the need for the const_cast, but ended up
deep in wild yak territory and gave up. I stuck with fixing all
the ancient style errors :)

BUG=302024

Review URL: https://codereview.chromium.org/182263002

git-svn-id: svn://svn.chromium.org/blink/trunk@167976 bbb929c8-8fbe-4397-9dbb-9b2b20218538