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

Review URL: https://codereview.chromium.org/147713002

git-svn-id: http://skia.googlecode.com/svn/trunk@13208 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed