use Make instead of Create to return a shared shader

src/core/SkReadBuffer.h

Index: src/core/SkReadBuffer.h
diff --git a/src/core/SkReadBuffer.h b/src/core/SkReadBuffer.h
index b9b30944fff0cc71b2c14d6526ef062e79f201bb..5db9f4644d46b2bfc9d5dc5fa103f26125455705 100644
--- a/src/core/SkReadBuffer.h
+++ b/src/core/SkReadBuffer.h
@@ -136,7 +136,7 @@ public:
     SkMaskFilter*  readMaskFilter()  { return this->readFlattenable<SkMaskFilter>(); }
     SkPathEffect*  readPathEffect()  { return this->readFlattenable<SkPathEffect>(); }
     SkRasterizer*  readRasterizer()  { return this->readFlattenable<SkRasterizer>(); }
-    SkShader*      readShader()      { return this->readFlattenable<SkShader>(); }
+    sk_sp<SkShader> readShader()     { return sk_sp<SkShader>(this->readFlattenable<SkShader>()); }
     SkXfermode*    readXfermode()    { return this->readFlattenable<SkXfermode>(); }
 
     /**