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

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index 2311bb75f4ef07d2b1c001a1c0bc8efc787635e4..0d4197fa68c10348420b568538691f29695b4c55 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -50,16 +50,12 @@ bool SkXfermodeImageFilter::onFilterImage(Proxy* proxy,
                                             SkBitmap* dst,
                                             SkIPoint* offset) const {
     SkBitmap background = src, foreground = src;
-    SkImageFilter* backgroundInput = this->getInput(0);
-    SkImageFilter* foregroundInput = this->getInput(1);
     SkIPoint backgroundOffset = SkIPoint::Make(0, 0);
-    if (backgroundInput &&
-        !backgroundInput->filterImage(proxy, src, ctx, &background, &backgroundOffset)) {
+    if (!this->filterInput(0, proxy, src, ctx, &background, &backgroundOffset)) {
         background.reset();
     }
     SkIPoint foregroundOffset = SkIPoint::Make(0, 0);
-    if (foregroundInput &&
-        !foregroundInput->filterImage(proxy, src, ctx, &foreground, &foregroundOffset)) {
+    if (!this->filterInput(1, proxy, src, ctx, &foreground, &foregroundOffset)) {
         foreground.reset();
     }