remove external header for SkModeColorFilter

src/core/SkModeColorFilter.h

 /*
- * Copyright 2015 Google Inc.
+ * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+#include "SkColorFilter.h"
+#include "SkXfermode.h"
+
 #ifndef SkModeColorFilter_DEFINED
 #define SkModeColorFilter_DEFINED
 
-#include "SkColorFilter.h"
-#include "SkColorPriv.h"
-#include "SkString.h"
-#include "SkXfermode.h"
-
 class SkModeColorFilter : public SkColorFilter {
 public:
     static SkColorFilter* Create(SkColor color, SkXfermode::Mode mode) {
         return new SkModeColorFilter(color, mode);
     }
 
     SkColor getColor() const { return fColor; }
     SkXfermode::Mode getMode() const { return fMode; }
     SkPMColor getPMColor() const { return fPMColor; }
 
     bool asColorMode(SkColor*, SkXfermode::Mode*) const override;
     uint32_t getFlags() const override;
     void filterSpan(const SkPMColor shader[], int count, SkPMColor result[]) const override;
 
 #ifndef SK_IGNORE_TO_STRING
-    void toString(SkString* str) const override {
-        str->append("SkModeColorFilter: color: 0x");
-        str->appendHex(fColor);
-        str->append(" mode: ");
-        str->append(SkXfermode::ModeName(fMode));
-    }
+    void toString(SkString* str) const override;
 #endif
 
 #if SK_SUPPORT_GPU
     const GrFragmentProcessor* asFragmentProcessor(GrContext*) const override;
 #endif
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkModeColorFilter)
 
 protected:
     SkModeColorFilter(SkColor color, SkXfermode::Mode mode) {
         fColor = color;
         fMode = mode;
         this->updateCache();
     };
 
     void flatten(SkWriteBuffer&) const override;
 
 private:
     SkColor             fColor;
     SkXfermode::Mode    fMode;
     // cache
     SkPMColor           fPMColor;
     SkXfermodeProc      fProc;
 
     void updateCache();
 
+    friend class SkColorFilter;
+
     typedef SkColorFilter INHERITED;
 };
 
 #endif