Revert of Unwrap GrRedBlackTree unit test and use REPORTER_ASSERT().

Revert of Unwrap GrRedBlackTree unit test and use REPORTER_ASSERT(). (https://codereview.chromium.org/147713002/)

Reason for revert:
broke http://108.170.217.252:10115/builders/Build-Mac10.8-Clang-x86_64-Release/builds/2908/steps/Retry_BuildTests/logs/stdio and other builders:

GrRedBlackTreeTest.cpp:24:36: error: use of undeclared identifier 'xi'


Original issue's description:
> Unwrap GrRedBlackTree unit test and use REPORTER_ASSERT().
> 
> This fixes the mtklein's TODO in GrUnitTests.cpp.
> 
> BUG=None
> TEST=out/Debug/tests
> R=mtklein@google.com, robertphillips@google.com
> 
> Committed: https://code.google.com/p/skia/source/detail?r=13208

TBR=mtklein@google.com,robertphillips@google.com,reed@google.com,tfarina@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=None

Committed: http://code.google.com/p/skia/source/detail?r=13209

[epoger, 2014-01-27 21:53:52]

Created Revert of Unwrap GrRedBlackTree unit test and use REPORTER_ASSERT().

[commit-bot: I haz the power, 2014-01-27 21:54:00]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/epoger@google.com/148653002/1

[commit-bot: I haz the power, 2014-01-27 21:54:33]

Change committed as 13209