add isRect() check to AAClip, to detect if a soft-clip is really just an irect

src/core/SkRasterClip.h

Index: src/core/SkRasterClip.h
diff --git a/src/core/SkRasterClip.h b/src/core/SkRasterClip.h
index 0c2723314ccb3cc9fe1e3651990c0b8797456b13..29a925f2a283ade5ebc0d0125e40a1d4a2212deb 100644
--- a/src/core/SkRasterClip.h
+++ b/src/core/SkRasterClip.h
@@ -89,11 +89,19 @@ private:
     }
 
     bool computeIsRect() const {
-        return fIsBW ? fBW.isRect() : false;
+        return fIsBW ? fBW.isRect() : fAA.isRect();
     }
 
-    bool updateCacheAndReturnNonEmpty() {
+    bool updateCacheAndReturnNonEmpty(bool detectAARect = true) {
         fIsEmpty = this->computeIsEmpty();
+
+        // detect that our computed AA is really just a (hard-edged) rect
+        if (detectAARect && !fIsEmpty && !fIsBW && fAA.isRect()) {
+            fBW.setRect(fAA.getBounds());
+            fAA.setEmpty(); // don't need this guy anymore
+            fIsBW = true;
+        }
+
         fIsRect = this->computeIsRect();
         return !fIsEmpty;
     }