Image Filters: refactor all CPU input processing into a filterInput helper function.

src/effects/SkMatrixConvolutionImageFilter.cpp

Index: src/effects/SkMatrixConvolutionImageFilter.cpp
diff --git a/src/effects/SkMatrixConvolutionImageFilter.cpp b/src/effects/SkMatrixConvolutionImageFilter.cpp
index b2780578e6c0607a027173e74822d1d43f596dd7..67813fd25910ac4f4ef1204cf91345cf6d94f9ca 100644
--- a/src/effects/SkMatrixConvolutionImageFilter.cpp
+++ b/src/effects/SkMatrixConvolutionImageFilter.cpp
@@ -268,7 +268,7 @@ bool SkMatrixConvolutionImageFilter::onFilterImage(Proxy* proxy,
                                                    SkIPoint* offset) const {
     SkBitmap src = source;
     SkIPoint srcOffset = SkIPoint::Make(0, 0);
-    if (getInput(0) && !getInput(0)->filterImage(proxy, source, ctx, &src, &srcOffset)) {
+    if (!this->filterInput(0, proxy, source, ctx, &src, &srcOffset)) {
         return false;
     }