flag to use const& instead of const* for src-rect

BUG=skia:

Review URL: https://codereview.chromium.org/1272713005
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index b0e7b8f..7c378c9 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -534,7 +534,7 @@
     lua2rect(L, 4, &dstR);
 
     SkPaint paint;
-    canvas->drawImageRect(image, srcRPtr, dstR, lua2OptionalPaint(L, 5, &paint));
+    canvas->legacy_drawImageRect(image, srcRPtr, dstR, lua2OptionalPaint(L, 5, &paint));
     return 0;
 }