We should add a visual indicator in the call tree at the edge of libraries

[julienw]

See the following capture:

In a stack we have nodes from both xul.pdb and DWrite.pdb. At other places we have other libraries like user32.pdb or ExplorerFrame.pdb.

Ideas:

• change the background color for different libraries
• change the color for the lib name text
• add an horizontal colored line at the node edge

┆Issue is synchronized with this Jira Task

[julienw]

(idea came from a discussion with @fqueze)