add helper makeShader for the common Clamp case

Bug: skia:
Change-Id: I22cac56f35fed16daede0cf1b3e34dfa6f5ae3ea
Reviewed-on: https://skia-review.googlesource.com/14625
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gm/drawatlas.cpp b/gm/drawatlas.cpp
index d0609b5..de44b6d 100644
--- a/gm/drawatlas.cpp
+++ b/gm/drawatlas.cpp
@@ -220,8 +220,7 @@
                 canvas->drawAtlas(image, &xform, &tex, &color, 1,
                                   mode, &tex, &paint);
                 canvas->translate(128, 0);
-                paint.setShader(image->makeShader(SkShader::kClamp_TileMode,
-                                                  SkShader::kClamp_TileMode));
+                paint.setShader(image->makeShader());
                 canvas->drawVertices(verts, mode, paint);
                 paint.setShader(nullptr);
                 canvas->translate(145, 0);