Re-land "Fix external SkImageFilter caching with clips."

src/core/SkImageFilter.cpp

Index: src/core/SkImageFilter.cpp
diff --git a/src/core/SkImageFilter.cpp b/src/core/SkImageFilter.cpp
index 6356c1a5dd0ab33fb9d49f9baf813631317f44f8..4c4b56beace2f60b9ff858e70c76cd6c1f3b2cd7 100644
--- a/src/core/SkImageFilter.cpp
+++ b/src/core/SkImageFilter.cpp
@@ -122,6 +122,16 @@ bool SkImageFilter::filterBounds(const SkIRect& src, const SkMatrix& ctm,
                                  SkIRect* dst) const {
     SkASSERT(&src);
     SkASSERT(dst);
+    if (SkImageFilter::GetExternalCache()) {
+        /*
+         *  When the external cache is active, do not intersect the saveLayer
+         *  bounds with the clip bounds. This is so that the cached result
+         *  is always the full size of the primitive's bounds,
+         *  regardless of the clip active on first draw.
+         */
+        *dst = SkIRect::MakeLargest();
+        return true;
+    }
     return this->onFilterBounds(src, ctm, dst);
 }