Don't leak the shader by reffing twice in SkRectShaderImageFilter.

BUG=skia:
R=bsalomon@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/501563002
diff --git a/src/effects/SkRectShaderImageFilter.cpp b/src/effects/SkRectShaderImageFilter.cpp
index fe0be12..be3c23c 100644
--- a/src/effects/SkRectShaderImageFilter.cpp
+++ b/src/effects/SkRectShaderImageFilter.cpp
@@ -44,7 +44,8 @@
 
 SkFlattenable* SkRectShaderImageFilter::CreateProc(SkReadBuffer& buffer) {
     SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 0);
-    return Create(buffer.readShader(), &common.cropRect());
+    SkAutoTUnref<SkShader> shader(buffer.readShader());
+    return Create(shader.get(), &common.cropRect());
 }
 
 void SkRectShaderImageFilter::flatten(SkWriteBuffer& buffer) const {