Sk4fLinearGradient fuzzer fixes

gm/gradients.cpp

Index: gm/gradients.cpp
diff --git a/gm/gradients.cpp b/gm/gradients.cpp
index 45b6564a64e0ff71ba55af08acfbf047d70a32fe..8ae1dd7901e45cd6044ca2968b7b8cb8cba324c9 100644
--- a/gm/gradients.cpp
+++ b/gm/gradients.cpp
@@ -919,3 +919,20 @@ DEF_SIMPLE_GM(gradient_many_stops, canvas, 500, 500) {
 DEF_SIMPLE_GM(gradient_many_stops_4f, canvas, 500, 500) {
     draw_many_stops(canvas, SkLinearGradient::kForce4fContext_PrivateFlag);
 }
+
+static void draw_subpixel_gradient(SkCanvas* canvas, uint32_t flags) {
+    const SkPoint pts[] = { {50, 50}, {50.1f, 50.1f}};
+    SkColor colors[] = { SK_ColorRED, SK_ColorGREEN, SK_ColorBLUE };
+    SkPaint p;
+    p.setShader(SkGradientShader::MakeLinear(
+        pts, colors, nullptr, SK_ARRAY_COUNT(colors), SkShader::kRepeat_TileMode, flags, nullptr));
+    canvas->drawRect(SkRect::MakeXYWH(0, 0, 500, 500), p);
+}
+
+DEF_SIMPLE_GM(gradient_subpixel, canvas, 500, 500) {
+    draw_subpixel_gradient(canvas, 0);
+}
+
+DEF_SIMPLE_GM(gradient_subpixel_4f, canvas, 500, 500) {
+    draw_subpixel_gradient(canvas, SkLinearGradient::kForce4fContext_PrivateFlag);
+}