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This patch fixes Japanese line breaking rules before and after ruby
elements. This patch is a port of http://wkb.ug/91588 with the
following changes:
* The WebKit patch sets ruby base text to the prior context for breaks
  after the ruby. Since U+FFFD Object Replacement Character can cover
  most of the common cases that this patch does not include that part.
* canBreakBefore() is fixed to include the correct UAX#14[1] classes
  that prohibit line breaks after. The original patch is a mix of
  before and after, and lacks some important after classes.

This patch fixes the common use cases in CJK, but it's hard to say this
is the right way to fix. There are two issues that block doing so at
this moment:
1. RubyRun is LayoutBlockFlow, but after WebKit implemented, the ruby
   spec was updated to allow line breaking within ruby, so it should be
   like inline, not a replaced element.
2. The CSS WG discussed on line breaking around replaced elements, but
   the discussion is not making much progress.
Changes in this patch should be updated when these issues are resolved.

[1] http://unicode.org/reports/tr14/

BUG=522826

Review URL: https://codereview.chromium.org/1304993003

git-svn-id: svn://svn.chromium.org/blink/trunk@201073 bbb929c8-8fbe-4397-9dbb-9b2b20218538