GitLab

- This improves and simplifies the tests covered in RemoveAllNodes.

BUG=None
TEST=app_unittests --gtest_filter=TreeNodeModelTest.RemoveAllNodes

R=sky@chromium.org

Review URL: http://codereview.chromium.org/7134061

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@88672 0039d316-1c4b-4281-b951-d872f2087c98