don't memtion SkXfermode in public

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=5070

Change-Id: Ia9527bfd0f13146669df5e71098af903e14bae3a
Reviewed-on: https://skia-review.googlesource.com/5070
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/include/core/SkBitmapDevice.h b/include/core/SkBitmapDevice.h
index 46269c3..17cb984 100644
--- a/include/core/SkBitmapDevice.h
+++ b/include/core/SkBitmapDevice.h
@@ -29,7 +29,6 @@
 class SkPixmap;
 class SkRRect;
 class SkSurface;
-class SkXfermode;
 struct SkPoint;
 
 ///////////////////////////////////////////////////////////////////////////////
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index ba8a383..95667e4 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -18,7 +18,6 @@
 #include "SkRefCnt.h"
 #include "SkRegion.h"
 #include "SkSurfaceProps.h"
-#include "SkXfermode.h"
 #include "SkLights.h"
 #include "../private/SkShadowParams.h"
 
diff --git a/include/core/SkColorFilter.h b/include/core/SkColorFilter.h
index a194927..fd3ccbc 100644
--- a/include/core/SkColorFilter.h
+++ b/include/core/SkColorFilter.h
@@ -8,10 +8,10 @@
 #ifndef SkColorFilter_DEFINED
 #define SkColorFilter_DEFINED
 
+#include "SkBlendMode.h"
 #include "SkColor.h"
 #include "SkFlattenable.h"
 #include "SkRefCnt.h"
-#include "SkXfermode.h"
 
 class GrContext;
 class GrFragmentProcessor;
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index ace98fa..de3b479 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -12,7 +12,7 @@
 #include "SkColor.h"
 #include "SkFilterQuality.h"
 #include "SkMatrix.h"
-#include "SkXfermode.h"
+#include "SkRefCnt.h"
 
 class SkAutoDescriptor;
 class SkAutoGlyphCache;
@@ -1056,7 +1056,7 @@
     SkColor         fColor;
     SkScalar        fWidth;
     SkScalar        fMiterLimit;
-    uint32_t        fBlendMode; // just need 5-6 bits for SkXfermode::Mode
+    uint32_t        fBlendMode; // just need 5-6 bits
     union {
         struct {
             // all of these bitfields should add up to 32