hide trivial helpers on canvas

BUG=skia:

Change-Id: I42d4ca92897bde5bd8e0575a0104b12b83134cef
Reviewed-on: https://skia-review.googlesource.com/8852
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/imagescalealigned.cpp b/gm/imagescalealigned.cpp
index 9498d32..3d74f0e 100644
--- a/gm/imagescalealigned.cpp
+++ b/gm/imagescalealigned.cpp
@@ -85,8 +85,11 @@
 
         paint.setColor(SK_ColorBLACK);
         surface->getCanvas()->drawLine(start.x(), start.y(), end.x(), end.y(), paint);
-        surface->getCanvas()->drawPoint(start.x(), start.y(), color);
-        surface->getCanvas()->drawPoint(end.x(), end.y(), color);
+
+        paint.reset();
+        paint.setColor(color);
+        const SkPoint pts[] = { start, end };
+        surface->getCanvas()->drawPoints(SkCanvas::kPoints_PointMode, 2, pts, paint);
 
         return surface->makeImageSnapshot();
     }