Merge pull request #271 from Unity-Technologies/zxw/support_editor_dragdrop

text background color bug fix

com.unity.uiwidgets/Runtime/painting/text_style.cs

         }
 
         public ui.TextStyle getTextStyle(float textScaleFactor = 1.0f) {
-            var backgroundPaint = new Paint();
-            if (background != null) {
-                backgroundPaint = new Paint();
-                backgroundPaint.color = backgroundColor;
-            }
-
             return new ui.TextStyle(
                 color: color,
                 decoration: decoration,
                 // locale: locale,
                 foreground: foreground,
                 background: background ?? (backgroundColor != null
-                    ? backgroundPaint
+                    ? new Paint {color = backgroundColor}
                     : null
                 ),
                 shadows: shadows?.Cast<Shadow>().ToList(),