Merge pull request #244 from Unity-Technologies/fix_sliver_bug

add devicePixelRatioEditorOnlyOverride to EditorPanel

com.unity.uiwidgets/Editor/UIWidgetsEditorPanel.cs

             get { return Mathf.RoundToInt(f: position.size.y); }
         }
 
+        protected float? devicePixelRatioEditorOnlyOverride = null;
+
-            get { return EditorGUIUtility.pixelsPerPoint; }
+            get {
+                return devicePixelRatioEditorOnlyOverride ?? EditorGUIUtility.pixelsPerPoint; }
         }
 
         void Update() {