Plumb through out_row byte length so we can assert we stay underneath it.

src/core/SkConvolver.cpp

Index: src/core/SkConvolver.cpp
diff --git a/src/core/SkConvolver.cpp b/src/core/SkConvolver.cpp
index 49688db03de8da2aea397caf23ba99a9e7d1c74f..bf00956b3ad6c08a43952d0408f5f7ac3d507cfd 100644
--- a/src/core/SkConvolver.cpp
+++ b/src/core/SkConvolver.cpp
@@ -436,7 +436,7 @@ void BGRAConvolve2D(const unsigned char* sourceData,
                     src[i] = &sourceData[(uint64_t)(nextXRow + i) * sourceByteRowStride];
                     outRow[i] = rowBuffer.advanceRow();
                 }
-                convolveProcs.fConvolve4RowsHorizontally(src, filterX, outRow);
+                convolveProcs.fConvolve4RowsHorizontally(src, filterX, outRow, 4*rowBufferWidth);
                 nextXRow += 4;
             } else {
                 // Check if we need to avoid SSE2 for this row.