Use SkBitmapProcStateAutoMapper for filter samplers also

src/core/SkBitmapProcState_shaderproc.h

Index: src/core/SkBitmapProcState_shaderproc.h
diff --git a/src/core/SkBitmapProcState_shaderproc.h b/src/core/SkBitmapProcState_shaderproc.h
index d41ff063e4dab72716ecb3be4e35c97f84c68678..1ff2e6bf2480f067499e59b7461fb7b69217e049 100644
--- a/src/core/SkBitmapProcState_shaderproc.h
+++ b/src/core/SkBitmapProcState_shaderproc.h
@@ -31,10 +31,8 @@ void SCALE_FILTER_NAME(const void* sIn, int x, int y, SkPMColor* SK_RESTRICT col
     unsigned subY;
 
     {
-        SkPoint pt;
-        s.fInvProc(s.fInvMatrix, SkIntToScalar(x) + SK_ScalarHalf,
-                   SkIntToScalar(y) + SK_ScalarHalf, &pt);
-        SkFixed fy = SkScalarToFixed(pt.fY) - (s.fFilterOneY >> 1);
+        const SkBitmapProcStateAutoMapper mapper(s, x, y);
+        SkFixed fy = SkFractionalIntToFixed(mapper.y());
         const unsigned maxY = s.fPixmap.height() - 1;
         // compute our two Y values up front
         subY = TILEY_LOW_BITS(fy, maxY);
@@ -46,7 +44,7 @@ void SCALE_FILTER_NAME(const void* sIn, int x, int y, SkPMColor* SK_RESTRICT col
         row0 = (const SRCTYPE*)(srcAddr + y0 * rb);
         row1 = (const SRCTYPE*)(srcAddr + y1 * rb);
         // now initialize fx
-        fx = SkScalarToFixed(pt.fX) - (oneX >> 1);
+        fx = SkFractionalIntToFixed(mapper.x());
     }
 
 #ifdef PREAMBLE