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;