Cleanup SkPicture* classes a bit

include/core/SkPicture.h

Index: include/core/SkPicture.h
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index 46521363760f877471d3e7ed4df639bb4ceb307b..ca26eb44962c381687b13fa5d44beffa3addef16 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -280,14 +280,11 @@ private:
     void createHeader(SkPictInfo* info) const;
     static bool IsValidPictInfo(const SkPictInfo& info);
 
-    friend class SkFlatPicture;
-    friend class SkPictureData;
-    friend class SkPictureRecorder; // just for SkPicture-based constructor
-    friend class SkGpuDevice;
-    friend class GrGatherCanvas;
-    friend class GrGatherDevice;
-    friend class SkDebugCanvas;
-    friend class SkPicturePlayback; // to get fData
+    friend class SkPictureData;                // to access OperationList
+    friend class SkPictureRecorder;            // just for SkPicture-based constructor
+    friend class SkGpuDevice;                  // for EXPERIMENTAL_getActiveOps/OperationList
+    friend class GrGatherCanvas;               // needs to know if old or new picture
+    friend class SkPicturePlayback;            // to get fData & OperationList
     friend class SkPictureReplacementPlayback; // to access OperationList
 
     typedef SkRefCnt INHERITED;