remove unneeded preroll

src/core/SkBitmapProcShader.cpp

Index: src/core/SkBitmapProcShader.cpp
diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index e6ed1136c0e8066105c94a276aab3a680e1bc3af..456e0d492087d29d84070ee1590b9a5da352aedc 100644
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -112,12 +112,6 @@ size_t SkBitmapProcShader::contextSize() const {
     return sizeof(BitmapProcShaderContext) + sizeof(SkBitmapProcState);
 }
 
-void SkBitmapProcShader::onPreroll() const {
-    SkBitmap bm(fRawBitmap);
-    bm.lockPixels();
-    bm.unlockPixels();
-}
-
 SkBitmapProcShader::BitmapProcShaderContext::BitmapProcShaderContext(
         const SkBitmapProcShader& shader, const ContextRec& rec, SkBitmapProcState* state)
     : INHERITED(shader, rec)