struct and class forward declarations incompatible on some compilers

git-svn-id: http://skia.googlecode.com/svn/trunk@10211 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkBitmapProcState.h b/src/core/SkBitmapProcState.h
index 3c8e346..6df683f 100644
--- a/src/core/SkBitmapProcState.h
+++ b/src/core/SkBitmapProcState.h
@@ -31,7 +31,7 @@
 #endif
 
 class SkPaint;
-class SkConvolutionProcs;
+struct SkConvolutionProcs;
 
 struct SkBitmapProcState {