ui/base/models: Avoid an unnecessary tmp variable in TreeNode::GetTotalNodeCount().
ui/base/models: Avoid an unnecessary tmp variable in TreeNode::GetTotalNodeCount().

Unrelated changes:
- Use the member variable |parent_| directly instead of calling the getter accessor |parent()|.
- Tweak some comments. Use node instead of Node to be more consistent.

BUG=None
TEST=out/Debug/app_unittests --gtest_filter=TreeNodeModelTest.GetTotalNodeCount

R=sky@chromium.org

Review URL: http://codereview.chromium.org/6975054

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@87481 0039d316-1c4b-4281-b951-d872f2087c98

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