Bug 208093 Make tree body frame cache row count r=varga sr=jag

layout/xul/base/src/tree/src/nsTreeBodyFrame.h

@@ -526,8 +526,6 @@ protected: // Data Members
 
   PRPackedBool mVerticalOverflow;
 
-  PRInt16 mUpdateBatchNest;
-
   // A guard that prevents us from recursive painting.
   PRPackedBool mImageGuard;
 
@@ -550,6 +548,9 @@ protected: // Data Members
   // A value array used to keep track of all spring loaded folders.
   nsValueArray mValueArray;
 
-  PRInt32 mCountBeforeUpdate;
+  PRInt32 mUpdateBatchNest;
+
+  // Cached row count.
+  PRInt32 mRowCount;
 
 }; // class nsTreeBodyFrame