SkTextBlob plumbing

Add SkTextBlob serialization + drawTextBlob() overrides.

R=mtklein@google.com, reed@google.com, robertphillips@google.com
BUG=269080

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/499413002
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index d436bd4..90fd017 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -265,6 +265,14 @@
     }
 }
 
+void SkNWayCanvas::onDrawTextBlob(const SkTextBlob* blob, SkScalar x, SkScalar y,
+                                  const SkPaint &paint) {
+    Iter iter(fList);
+    while (iter.next()) {
+        iter->drawTextBlob(blob, x, y, paint);
+    }
+}
+
 void SkNWayCanvas::onDrawPicture(const SkPicture* picture, const SkMatrix* matrix,
                                  const SkPaint* paint) {
     Iter iter(fList);