Fix [Object object] appearing on surfaceflinger trace

When traversing tree of the transformObject, _transform function with
some fields did not have a key and instead had a terminal class. This
has been updated to display the key string.

Bug: 190176285

Test: Using a pb file giving a object object previously and clicking
show diff on all, see that no object object appears now.

Change-Id: I7fa3db3a631209e1d5e1f771a93d7b3e57694309
1 file changed