ProgramExplorer outline nodes jump to "-patch" directory script

[migueltylee]

When certain 'function' object nodes are selected in the Program Explorer outline, the SourceLocation of the function is in a _patch file, thus the file explorer will jump to the patch file. This is a way to reproduce the issue:

• In the ProgramExplorer library dart:async select the script async_error.dart
• In the outline expand the AsyncError class and select the _stackTrace function
• The program will then fetch the source script for that object when calling node.populateLocation() and the file explorer goes there after calling showScripLocation.