Image filters: Make a recursive, forward-mapping bounds traversal.

src/effects/SkMergeImageFilter.cpp

Index: src/effects/SkMergeImageFilter.cpp
diff --git a/src/effects/SkMergeImageFilter.cpp b/src/effects/SkMergeImageFilter.cpp
index 2ae8b35cd023140f5fe62f74348f25e9281916cf..12fff9533a50b00651e1d967a14edec61db1c4e9 100755
--- a/src/effects/SkMergeImageFilter.cpp
+++ b/src/effects/SkMergeImageFilter.cpp
@@ -92,7 +92,8 @@ bool SkMergeImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& src,
     }
 
     // Apply the crop rect to the union of the inputs' bounds.
-    if (!this->getCropRect().applyTo(bounds, ctx, &bounds)) {
+    this->getCropRect().applyTo(bounds, ctx.ctm(), &bounds);
+    if (!bounds.intersect(ctx.clipBounds())) {
         return false;
     }