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/SkProxyCanvas.cpp b/src/utils/SkProxyCanvas.cpp
index 20f9307..5cb5469 100644
--- a/src/utils/SkProxyCanvas.cpp
+++ b/src/utils/SkProxyCanvas.cpp
@@ -136,7 +136,7 @@
     fProxy->drawTextOnPath(text, byteLength, path, matrix, paint);
 }
 
-void SkProxyCanvas::drawPicture(SkPicture& picture) {
+void SkProxyCanvas::onDrawPicture(const SkPicture* picture) {
     fProxy->drawPicture(picture);
 }