make SkComposeShader.h private

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1697523003

Review URL: https://codereview.chromium.org/1697523003
diff --git a/samplecode/PerlinPatch.cpp b/samplecode/PerlinPatch.cpp
index 9bb95e5..de4d451 100644
--- a/samplecode/PerlinPatch.cpp
+++ b/samplecode/PerlinPatch.cpp
@@ -11,7 +11,6 @@
 #include "SkGradientShader.h"
 #include "SkPatchUtils.h"
 #include "SkPerlinNoiseShader2/SkPerlinNoiseShader2.h"
-#include "SkComposeShader.h"
 
 static void draw_control_points(SkCanvas* canvas, const SkPoint cubics[12]) {
     //draw control points
@@ -148,7 +147,7 @@
         SkScalar scaleFreq = 2.0;
         fShader1 = SkPerlinNoiseShader2::CreateImprovedNoise(fXFreq/scaleFreq, fYFreq/scaleFreq, 4,
                                                              fSeed);
-        fShaderCompose = new SkComposeShader(fShader0, fShader1);
+        fShaderCompose = SkShader::CreateComposeShader(fShader0, fShader1, nullptr);
 
         paint.setShader(fShaderCompose);
         canvas->drawPatch(fPts, nullptr, texCoords, xfer, paint);
diff --git a/samplecode/SampleAll.cpp b/samplecode/SampleAll.cpp
index ad3181f..addca35 100644
--- a/samplecode/SampleAll.cpp
+++ b/samplecode/SampleAll.cpp
@@ -28,7 +28,6 @@
 #include "SkPictureRecorder.h"
 #include "SkRegion.h"
 #include "SkShader.h"
-#include "SkComposeShader.h"
 #include "SkCornerPathEffect.h"
 #include "SkPathMeasure.h"
 #include "SkPicture.h"
@@ -511,7 +510,7 @@
         SkShader* shaderB = SkGradientShader::CreateLinear(pts, colors2, nullptr,
             2, SkShader::kClamp_TileMode);
         SkXfermode* mode = SkXfermode::Create(SkXfermode::kDstIn_Mode);
-        SkShader* result = new SkComposeShader(shaderA, shaderB, mode);
+        SkShader* result = SkShader::CreateComposeShader(shaderA, shaderB, mode);
         shaderA->unref();
         shaderB->unref();
         mode->unref();
diff --git a/samplecode/SampleArc.cpp b/samplecode/SampleArc.cpp
index 834ba90..3b5288d 100644
--- a/samplecode/SampleArc.cpp
+++ b/samplecode/SampleArc.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkComposeShader.h"
 #include "Sk1DPathEffect.h"
 #include "SkCornerPathEffect.h"
 #include "SkPathMeasure.h"
diff --git a/samplecode/SampleShaders.cpp b/samplecode/SampleShaders.cpp
index dd444ec..2c0a6ab 100644
--- a/samplecode/SampleShaders.cpp
+++ b/samplecode/SampleShaders.cpp
@@ -16,7 +16,6 @@
 #include "SkShader.h"
 #include "SkUtils.h"
 #include "SkXfermode.h"
-#include "SkComposeShader.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
@@ -38,7 +37,7 @@
 
     SkXfermode* mode = SkXfermode::Create(SkXfermode::kDstIn_Mode);
 
-    SkShader* shader = new SkComposeShader(shaderB, shaderA, mode);
+    SkShader* shader = SkShader::CreateComposeShader(shaderB, shaderA, mode);
     shaderA->unref();
     shaderB->unref();
     mode->unref();
@@ -71,7 +70,7 @@
 
         SkXfermode* mode = SkXfermode::Create(SkXfermode::kDstIn_Mode);
 
-        fShader = new SkComposeShader(shaderA, shaderB, mode);
+        fShader = SkShader::CreateComposeShader(shaderA, shaderB, mode);
         shaderA->unref();
         shaderB->unref();
         mode->unref();