Steps to reproduce:
1. Open attached project
2. Go to "UIElementsExamples"->"05_Controls"
3. Open Profiler window
4. In Profiler press "Profile Editor" and "Deep Profile" and select CPU section
5. Now hover on one of the "Test" labels(text part) in "Example 5" window
-StyleContext.ApplyStyles() is getting called even though no styles were changed (check in profiler)

Problem: StyleContext.ApplyStyles() is being called during most GUIUtility.ProcessEvent(), and takes a long time, causing the editor to slow down when many UIElements are being repainted.
Expected result: Style does not change when just hovering over an element, so it should not have to reapply them, taking up a lot of time

Note: Couldn't test on 2017.1 or lower because UIElements namespace doesn't exist until 2017.2

Reproduced on: 2017.2.0b4, 2017.3.0a1