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

src/effects/SkBlurImageFilter.cpp

Index: src/effects/SkBlurImageFilter.cpp
diff --git a/src/effects/SkBlurImageFilter.cpp b/src/effects/SkBlurImageFilter.cpp
index a867971a0c289bb5196be40d56691004a0a7d1da..ddc034d73ca0c40cbe32ced235e7472fbf8a168a 100644
--- a/src/effects/SkBlurImageFilter.cpp
+++ b/src/effects/SkBlurImageFilter.cpp
@@ -72,8 +72,7 @@ bool SkBlurImageFilter::onFilterImage(Proxy* proxy,
                                       SkBitmap* dst, SkIPoint* offset) const {
     SkBitmap src = source;
     SkIPoint srcOffset = SkIPoint::Make(0, 0);
-    if (this->getInput(0) &&
-        !this->getInput(0)->filterImage(proxy, source, ctx, &src, &srcOffset)) {
+    if (!this->filterInput(0, proxy, source, ctx, &src, &srcOffset)) {
         return false;
     }