Bug 1402246 - Remove "friend struct" declarations in nsStyleStruct.h. r=heycam

Those structs do not have any private section, so those "friend struct"
declarations are not needed.

MozReview-Commit-ID: BYPPPLAdiEQ

--HG--
extra : rebase_source : 58cb78f8d6f8c60c7345ece204326cf580d5905f

layout/style/nsStyleStruct.h

@@ -640,8 +640,6 @@ struct nsStyleImageLayers {
 
   static bool IsInitialPositionForLayerType(mozilla::Position aPosition, LayerType aType);
 
-  struct Size;
-  friend struct Size;
   struct Size {
     struct Dimension : public nsStyleCoord::CalcValue {
       nscoord ResolveLengthPercentage(nscoord aAvailable) const {
@@ -703,8 +701,6 @@ struct nsStyleImageLayers {
     }
   };
 
-  struct Repeat;
-  friend struct Repeat;
   struct Repeat {
     mozilla::StyleImageLayerRepeat mXRepeat, mYRepeat;
 
@@ -736,8 +732,6 @@ struct nsStyleImageLayers {
     }
   };
 
-  struct Layer;
-  friend struct Layer;
   struct Layer {
     typedef mozilla::StyleGeometryBox StyleGeometryBox;