Alter SkCanvas::drawPicture (devirtualize, take const SkPicture, take pointer)

R=reed@google.com, bsalomon@google.com, mtklein@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/313613004
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index 3c98e4b..505c05c 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -265,7 +265,7 @@
     }
 }
 
-void SkNWayCanvas::drawPicture(SkPicture& picture) {
+void SkNWayCanvas::onDrawPicture(const SkPicture* picture) {
     Iter iter(fList);
     while (iter.next()) {
         iter->drawPicture(picture);