Repro steps:
1. Create a new project
2. Remove everything in the manifest.json (including modules)
3. Add Timeline package

Expected Result: Project should compile normally
Actual Result: Compilation errors about missing GUIUtility

Reproducible with: 1.4.0, 1.4.5 (2019.4.17f1, 2020.1.17f1, 2020.2.1f1), 1.5.1-pre.3 (2021.1.0b1)
Not Reproducible with: 1.2.17, 1.3.6 (2019.4.17f1, 2020.1.17f1, 2020.2.1f1)

Notes: 1.2.17 and 1.3.6 cause Compilation errors due to Animation dependencies,
1.4.5 and above cause Compilation errors about missing GUIUtility