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/SampleEffects.cpp b/samplecode/SampleEffects.cpp
index b58d557..12ea4e2 100644
--- a/samplecode/SampleEffects.cpp
+++ b/samplecode/SampleEffects.cpp
@@ -40,8 +40,8 @@
 static void paint_proc3(SkPaint* paint) {
     SkColor colors[] = { SK_ColorRED, COLOR, SK_ColorBLUE };
     SkPoint pts[] = { { 3, 0 }, { 7, 5 } };
-    paint->setShader(SkGradientShader::CreateLinear(pts, colors, nullptr, SK_ARRAY_COUNT(colors),
-                                        SkShader::kMirror_TileMode))->unref();
+    paint->setShader(SkGradientShader::MakeLinear(pts, colors, nullptr, SK_ARRAY_COUNT(colors),
+                                                  SkShader::kMirror_TileMode));
 }
 
 static void paint_proc5(SkPaint* paint) {