Revert "Revert "make it illegal to include SkXfermode.h""

This reverts commit e9d1b299ccbf8017ba57040986ded638f954684a.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "make it illegal to include SkXfermode.h"
> 
> This reverts commit 07764cefbb18041a77897df3453903b0a2016583.
> 
> Reason for revert: breaking google3
> 
> Original change's description:
> > make it illegal to include SkXfermode.h
> > 
> > BUG=skia:
> > 
> > GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=5133
> > 
> > Change-Id: I6e8596dcb17cd7e8efa67859bb682bf9bfcac4db
> > Reviewed-on: https://skia-review.googlesource.com/5133
> > Reviewed-by: Mike Reed <reed@google.com>
> > Commit-Queue: Mike Reed <reed@google.com>
> > 
> 
> TBR=reed@google.com,reviews@skia.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> 
> Change-Id: I136f9e533eb60633c49dffa19b5747d50b6d98a8
> Reviewed-on: https://skia-review.googlesource.com/5196
> Commit-Queue: Greg Daniel <egdaniel@google.com>
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> 

TBR=egdaniel@google.com,reviews@skia.org,reed@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I0b767ce778a4ade83c2f07d5ece486bb46d7712c
Reviewed-on: https://skia-review.googlesource.com/5223
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/samplecode/ClockFaceView.cpp b/samplecode/ClockFaceView.cpp
index 9cee95b..2721a5b 100644
--- a/samplecode/ClockFaceView.cpp
+++ b/samplecode/ClockFaceView.cpp
@@ -164,10 +164,7 @@
 
 typedef void (*raster_proc)(SkLayerRasterizer*, SkPaint&);
 
-#include "SkXfermode.h"
-
-static void apply_shader(SkPaint* paint, float scale)
-{
+static void apply_shader(SkPaint* paint, float scale) {
     SkPaint p;
     SkLayerRasterizer::Builder rastBuilder;
 
diff --git a/samplecode/SampleAll.cpp b/samplecode/SampleAll.cpp
index 94c12cd..fc3a95a 100644
--- a/samplecode/SampleAll.cpp
+++ b/samplecode/SampleAll.cpp
@@ -32,7 +32,6 @@
 #include "SkRandom.h"
 #include "SkTypeface.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 
 #include <math.h>
 #include "DecodeFile.h"
diff --git a/samplecode/SampleAnimatedText.cpp b/samplecode/SampleAnimatedText.cpp
index 6bd6d82..dec8f8f 100644
--- a/samplecode/SampleAnimatedText.cpp
+++ b/samplecode/SampleAnimatedText.cpp
@@ -15,7 +15,6 @@
 #include "SkSystemEventTypes.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
 #include "Timer.h"
 
 #if SK_SUPPORT_GPU
diff --git a/samplecode/SampleBitmapRect.cpp b/samplecode/SampleBitmapRect.cpp
index 24c3eff..ebfe3bb 100644
--- a/samplecode/SampleBitmapRect.cpp
+++ b/samplecode/SampleBitmapRect.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleConcavePaths.cpp b/samplecode/SampleConcavePaths.cpp
index d75ec4c..7ff6819 100644
--- a/samplecode/SampleConcavePaths.cpp
+++ b/samplecode/SampleConcavePaths.cpp
@@ -14,7 +14,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkParsePath.h"
diff --git a/samplecode/SampleEmboss.cpp b/samplecode/SampleEmboss.cpp
index f1ea1fe..4aba6fd 100644
--- a/samplecode/SampleEmboss.cpp
+++ b/samplecode/SampleEmboss.cpp
@@ -21,7 +21,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
 
 class EmbossView : public SampleView {
     SkEmbossMaskFilter::Light   fLight;
diff --git a/samplecode/SampleFilter2.cpp b/samplecode/SampleFilter2.cpp
index 8c93563..9b2298a 100644
--- a/samplecode/SampleFilter2.cpp
+++ b/samplecode/SampleFilter2.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleFuzz.cpp b/samplecode/SampleFuzz.cpp
index c7d0578..a0cb0e0 100644
--- a/samplecode/SampleFuzz.cpp
+++ b/samplecode/SampleFuzz.cpp
@@ -10,7 +10,6 @@
 #include "SkBlurMaskFilter.h"
 #include "SkPaint.h"
 #include "SkPath.h"
-#include "SkXfermode.h"
 #include "SkMatrix.h"
 #include "SkColor.h"
 #include "SkRandom.h"
diff --git a/samplecode/SampleHairline.cpp b/samplecode/SampleHairline.cpp
index fef44f5..169804d 100644
--- a/samplecode/SampleHairline.cpp
+++ b/samplecode/SampleHairline.cpp
@@ -21,8 +21,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkStream.h"
 #include "SkColorPriv.h"
 
diff --git a/samplecode/SampleLayers.cpp b/samplecode/SampleLayers.cpp
index 71b2e8b..c086eb0 100644
--- a/samplecode/SampleLayers.cpp
+++ b/samplecode/SampleLayers.cpp
@@ -23,7 +23,6 @@
 #include "SkTypeface.h"
 #include "SkUtils.h"
 #include "SkKey.h"
-#include "SkXfermode.h"
 #include "SkDrawFilter.h"
 
 static void make_paint(SkPaint* paint, const SkMatrix& localMatrix) {
diff --git a/samplecode/SampleLines.cpp b/samplecode/SampleLines.cpp
index 08a9e86..bf43e8b 100644
--- a/samplecode/SampleLines.cpp
+++ b/samplecode/SampleLines.cpp
@@ -21,8 +21,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkStream.h"
 #include "SkColorPriv.h"
 
diff --git a/samplecode/SamplePatch.cpp b/samplecode/SamplePatch.cpp
index 243d106..b105090 100644
--- a/samplecode/SamplePatch.cpp
+++ b/samplecode/SamplePatch.cpp
@@ -17,7 +17,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SamplePath.cpp b/samplecode/SamplePath.cpp
index f0bdf8d..40c350f 100644
--- a/samplecode/SamplePath.cpp
+++ b/samplecode/SamplePath.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkParsePath.h"
diff --git a/samplecode/SamplePathClip.cpp b/samplecode/SamplePathClip.cpp
index af9608f..b425884 100644
--- a/samplecode/SamplePathClip.cpp
+++ b/samplecode/SamplePathClip.cpp
@@ -13,7 +13,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SamplePdfFileViewer.cpp b/samplecode/SamplePdfFileViewer.cpp
index 110aa58..ab5a73e 100644
--- a/samplecode/SamplePdfFileViewer.cpp
+++ b/samplecode/SamplePdfFileViewer.cpp
@@ -26,8 +26,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkPdfRenderer.h"
 
 class PdfFileViewer : public SampleView {
diff --git a/samplecode/SamplePictFile.cpp b/samplecode/SamplePictFile.cpp
index 83912a5..32cc723 100644
--- a/samplecode/SamplePictFile.cpp
+++ b/samplecode/SamplePictFile.cpp
@@ -25,8 +25,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkStream.h"
 #include "SkSurface.h"
 
diff --git a/samplecode/SamplePoints.cpp b/samplecode/SamplePoints.cpp
index 0bfe28f..13b9897 100644
--- a/samplecode/SamplePoints.cpp
+++ b/samplecode/SamplePoints.cpp
@@ -19,8 +19,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkStream.h"
 
 class PointsView : public SampleView {
diff --git a/samplecode/SampleShaders.cpp b/samplecode/SampleShaders.cpp
index ba3b80d..f9926eb 100644
--- a/samplecode/SampleShaders.cpp
+++ b/samplecode/SampleShaders.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleText.cpp b/samplecode/SampleText.cpp
index 730c47c..8325cd7 100644
--- a/samplecode/SampleText.cpp
+++ b/samplecode/SampleText.cpp
@@ -21,8 +21,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
-
 #include "SkStream.h"
 
 static const struct {
diff --git a/samplecode/SampleTextAlpha.cpp b/samplecode/SampleTextAlpha.cpp
index 48625ad..8286177 100644
--- a/samplecode/SampleTextAlpha.cpp
+++ b/samplecode/SampleTextAlpha.cpp
@@ -15,7 +15,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleTextBox.cpp b/samplecode/SampleTextBox.cpp
index 8540ca4..947ed8e 100644
--- a/samplecode/SampleTextBox.cpp
+++ b/samplecode/SampleTextBox.cpp
@@ -16,7 +16,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleVertices.cpp b/samplecode/SampleVertices.cpp
index 3ba98bb..d08726c 100644
--- a/samplecode/SampleVertices.cpp
+++ b/samplecode/SampleVertices.cpp
@@ -14,7 +14,6 @@
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
-#include "SkXfermode.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkTime.h"
diff --git a/samplecode/SampleXfermodesBlur.cpp b/samplecode/SampleXfermodesBlur.cpp
index fe07c9b..2169ffd 100644
--- a/samplecode/SampleXfermodesBlur.cpp
+++ b/samplecode/SampleXfermodesBlur.cpp
@@ -21,7 +21,6 @@
 #include "SkColorFilter.h"
 #include "SkTime.h"
 #include "SkTypeface.h"
-#include "SkXfermode.h"
 
 #include "SkStream.h"
 #include "SkColorPriv.h"