[FastTextAutosizer] Implement wide descendant autosizing

This patch enables autosizing for blocks that are wider than their
parent's DBCAT[1]. For example:
<div width="300px">
  [text that should not be autosized]
  <div width="800px">
    [text that should be autosized] <-- this patch makes this autosize
  </div>
</div>

Because the width of a block is not computable until the block is in
layout, a heuristic has been added to create potentially-autosizing
clusters (see: mightBeWiderDescendant). When computing a cluster's
multiplier we now check isWiderDescendant which will determine
whether a potentially-autosizing cluster should actually autosize,
or whether it should inherit its parent's multiplier.

With this patch we pass an additional 3 tests!

This patch also removes some unnecessary #ifndef's around ASSERT
statements.

[1] "Deepest Block Containing All Text".

BUG=302005
NOTRY=true

Review URL: https://codereview.chromium.org/147843002

git-svn-id: svn://svn.chromium.org/blink/trunk@165967 bbb929c8-8fbe-4397-9dbb-9b2b20218538