FIX: for degenerate tree with a single leave.

To render a tree with a single leave node,
the TriangleLookupTable range nneeds to be
modified.

Change-Id: If374953a8d658392cfd0f6bf5b5b620aa2dcea24
Another approach to fix this degenerate case

This commit resolves the error that were previously experiencing
when a tree was pruned down to a single leaf.  It does so without
changing the color lookup table for normal, collapsed leaves.  This
means that we do not have to update the baseline image to keep the
AutoCollapse test passing.

Change-Id: Idf4fc9e2f9ad2046f298623208769138c1bad841
Merge topic 'TreeHeatmapItemFix' into master

156390e9 Another approach to fix this degenerate case
110169fd FIX: for degenerate tree with a single leave.