Constify SkFlattenable::getFactory().

include/core/SkFlattenableBuffers.h

Index: include/core/SkFlattenableBuffers.h
diff --git a/include/core/SkFlattenableBuffers.h b/include/core/SkFlattenableBuffers.h
index 51016c737ffbc705b697809830c0ad0ab9164c5c..d71f7c025b6fbafc6631652440a67e3ef3247ee6 100644
--- a/include/core/SkFlattenableBuffers.h
+++ b/include/core/SkFlattenableBuffers.h
@@ -182,7 +182,7 @@ public:
                                     SkPaint::TextEncoding encoding) = 0;
 
     // common data structures
-    virtual void writeFlattenable(SkFlattenable* flattenable) = 0;
+    virtual void writeFlattenable(const SkFlattenable* flattenable) = 0;
     virtual void writeColor(const SkColor& color) = 0;
     virtual void writeColorArray(const SkColor* color, uint32_t count) = 0;
     virtual void writePoint(const SkPoint& point) = 0;
@@ -222,7 +222,7 @@ public:
 
 protected:
     // A helper function so that each subclass does not have to be a friend of SkFlattenable
-    void flattenObject(SkFlattenable* obj, SkFlattenableWriteBuffer& buffer);
+    void flattenObject(const SkFlattenable* obj, SkFlattenableWriteBuffer& buffer);
 
     uint32_t fFlags;
 };