Fix clip area behavior for REPLACE op

bug:22291400

Work around clippath-clipped-to-view-bounds behavior by
implementing REPLACE op fast path, avoiding the transition to
SkRegion/SkPath.

Change-Id: I63c1cf961db2d6e3759d83914de1036c9ac7497a
diff --git a/libs/hwui/ClipArea.h b/libs/hwui/ClipArea.h
index e284af0..51ef27b 100644
--- a/libs/hwui/ClipArea.h
+++ b/libs/hwui/ClipArea.h
@@ -153,6 +153,8 @@
     }
 
     void regionFromPath(const SkPath& path, SkRegion& pathAsRegion) {
+        // TODO: this should not mask every path to the viewport - this makes it impossible to use
+        // paths to clip to larger areas (which is valid e.g. with SkRegion::kReplace_Op)
         pathAsRegion.setPath(path, createViewportRegion());
     }