Create LineLayout api

Create LineLayout api

This is a first step in having the line layout code not talk directly to the LayoutObject hierarchy. Eventually, the plan is to fully isolate the LayoutObject hierarchy from the rest of the codebase (editing, DOM, paint, etc) and use include guards to enforce that. In this way, we can be explicit about not relying on implementation details outside of the box layout code.

This is implemented by creating a POD wrapper around the equivalent LayoutObject class and passing them around by value. This is similar to what the web/ classes do (e.g. WebNode) and we believe this will be extremely low overhead performance wise and strictly equivalent memory wise. In this patch, there happens to be a LayoutObject class for each LineLayout* wrapper class, but that's not required (or even desired) in the end. The first step here is to isolate all the code to make it explicit which parts of the box layout code line layout current needs and then in a followup step to take a step back and figure out what the desired end result is.

Not all files in the layout/line directory have been converted yet. Will occur in following patches.

[ikilpatrick, 2015-06-03 05:22:58]

ikilpatrick@chromium.org changed reviewers:
+ eae@chromium.org, leviw@chromium.org, ojan@chromium.org

[leviw_travelin_and_unemployed, 2015-06-03 19:05:42]

The CQ bit was checked by leviw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-06-03 19:06:47]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1149953007/100001

[commit-bot: I haz the power, 2015-06-03 20:24:42]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-03 20:24:43]

Dry run: Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/6...)

[ikilpatrick, 2015-06-04 11:15:54]

Removed crashes. There were some typos in InlineIterator.h which did
LayoutObject -> LineLayoutBlockFlow, instead of LayoutObject -> LineLayoutItem.

[pilgrim_google, 2015-06-08 14:00:48]

Rebased and continued in https://codereview.chromium.org/1164933006