use Make instead of Create to return a shared shader

Partially updated call sites. Undefine the flag in SkSHader.h to convert the remaining sites.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1772463002

Review URL: https://codereview.chromium.org/1772463002
diff --git a/samplecode/SampleTiling.cpp b/samplecode/SampleTiling.cpp
index ed244eb..125155e 100644
--- a/samplecode/SampleTiling.cpp
+++ b/samplecode/SampleTiling.cpp
@@ -35,15 +35,14 @@
     SkPaint     paint;
 
     paint.setDither(true);
-    paint.setShader(SkGradientShader::CreateLinear(pts, colors, pos,
-                SK_ARRAY_COUNT(colors), SkShader::kClamp_TileMode))->unref();
+    paint.setShader(SkGradientShader::MakeLinear(pts, colors, pos,
+                SK_ARRAY_COUNT(colors), SkShader::kClamp_TileMode));
     canvas.drawPaint(paint);
 }
 
 static void setup(SkPaint* paint, const SkBitmap& bm, bool filter,
                   SkShader::TileMode tmx, SkShader::TileMode tmy) {
-    SkShader* shader = SkShader::CreateBitmapShader(bm, tmx, tmy);
-    paint->setShader(shader)->unref();
+    paint->setShader(SkShader::MakeBitmapShader(bm, tmx, tmy));
     paint->setFilterQuality(filter ? kLow_SkFilterQuality : kNone_SkFilterQuality);
 }