Revert of change all factories to return their base-class

src/effects/SkMatrixConvolutionImageFilter.cpp

 /*
  * Copyright 2012 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMatrixConvolutionImageFilter.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 29 matching lines @@
     fTileMode(tileMode),
     fConvolveAlpha(convolveAlpha) {
     size_t size = (size_t) sk_64_mul(fKernelSize.width(), fKernelSize.height());
     fKernel = new SkScalar[size];
     memcpy(fKernel, kernel, size * sizeof(SkScalar));
     SkASSERT(kernelSize.fWidth >= 1 && kernelSize.fHeight >= 1);
     SkASSERT(kernelOffset.fX >= 0 && kernelOffset.fX < kernelSize.fWidth);
     SkASSERT(kernelOffset.fY >= 0 && kernelOffset.fY < kernelSize.fHeight);
 }
 
-SkImageFilter* SkMatrixConvolutionImageFilter::Create(
+SkMatrixConvolutionImageFilter* SkMatrixConvolutionImageFilter::Create(
     const SkISize& kernelSize,
     const SkScalar* kernel,
     SkScalar gain,
     SkScalar bias,
     const SkIPoint& kernelOffset,
     TileMode tileMode,
     bool convolveAlpha,
     SkImageFilter* input,
     const CropRect* cropRect) {
     if (kernelSize.width() < 1 || kernelSize.height() < 1) {
@@ skipping 327 matching lines @@
             str->appendf("%f ", fKernel[y * fKernelSize.width() + x]);
         }
     }
     str->appendf(")");
     str->appendf("gain: %f bias: %f ", fGain, fBias);
     str->appendf("offset: (%d, %d) ", fKernelOffset.fX, fKernelOffset.fY);
     str->appendf("convolveAlpha: %s", fConvolveAlpha ? "true" : "false");
     str->append(")");
 }
 #endif