extend modecolorfilter to 4f

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1670063002

Review URL: https://codereview.chromium.org/1670063002
diff --git a/gm/color4f.cpp b/gm/color4f.cpp
index e912654..9e6fcf6 100644
--- a/gm/color4f.cpp
+++ b/gm/color4f.cpp
@@ -45,10 +45,14 @@
     return SkColorFilter::CreateComposeFilter(a, b);
 }
 
+static SkColorFilter* make_cf2() {
+    return SkColorFilter::CreateModeFilter(0x8044CC88, SkXfermode::kSrcATop_Mode);
+}
+
 static void draw_into_canvas(SkCanvas* canvas) {
-    const SkRect r = SkRect::MakeWH(100, 100);
+    const SkRect r = SkRect::MakeWH(50, 100);
     SkShader* (*shaders[])() { make_opaque_color, make_alpha_color };
-    SkColorFilter* (*filters[])() { make_cf_null, make_cf0, make_cf1 };
+    SkColorFilter* (*filters[])() { make_cf_null, make_cf0, make_cf1, make_cf2 };
     
     SkPaint paint;
     for (auto shProc : shaders) {
@@ -56,13 +60,13 @@
         for (auto cfProc : filters) {
             SkSafeUnref(paint.setColorFilter(cfProc()));
             canvas->drawRect(r, paint);
-            canvas->translate(120, 0);
+            canvas->translate(60, 0);
         }
     }
 }
 
-DEF_SIMPLE_GM(color4f, canvas, 620, 260) {
-    canvas->translate(20, 20);
+DEF_SIMPLE_GM(color4f, canvas, 1024, 260) {
+    canvas->translate(10, 10);
 
     SkPaint bg;
     // need the target to be opaque, so we can draw it to the screen
@@ -71,7 +75,7 @@
 
     SkColorProfileType const profiles[] { kLinear_SkColorProfileType, kSRGB_SkColorProfileType };
     for (auto profile : profiles) {
-        const SkImageInfo info = SkImageInfo::Make(600, 100, kN32_SkColorType, kPremul_SkAlphaType,
+        const SkImageInfo info = SkImageInfo::Make(1024, 100, kN32_SkColorType, kPremul_SkAlphaType,
                                                    profile);
         SkAutoTUnref<SkSurface> surface(SkSurface::NewRaster(info));
         surface->getCanvas()->drawPaint(bg);