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/rectangletexture.cpp b/gm/rectangletexture.cpp
index d4f4552..67ffa9a 100644
--- a/gm/rectangletexture.cpp
+++ b/gm/rectangletexture.cpp
@@ -163,8 +163,7 @@
 
                 SkPaint clampPaint;
                 clampPaint.setFilterQuality(q);
-                clampPaint.setShader(rectImg->makeShader(SkShader::kClamp_TileMode,
-                                                         SkShader::kClamp_TileMode));
+                clampPaint.setShader(rectImg->makeShader());
                 canvas->drawRect(SkRect::MakeWH(1.5f * kWidth, 1.5f * kHeight), clampPaint);
                 canvas->translate(kWidth * 1.5f + kPad, 0);