add isAlphaOnly() query

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 149 matching lines @@
     static sk_sp<SkImage> MakeTextureFromPixmap(GrContext*, const SkPixmap&, SkBudgeted budgeted);
 
     ///////////////////////////////////////////////////////////////////////////////////////////////
 
     int width() const { return fWidth; }
     int height() const { return fHeight; }
     SkISize dimensions() const { return SkISize::Make(fWidth, fHeight); }
     SkIRect bounds() const { return SkIRect::MakeWH(fWidth, fHeight); }
     uint32_t uniqueID() const { return fUniqueID; }
     SkAlphaType alphaType() const;
+
+    /**

[robertphillips, 2016/10/31 17:18:13]

fi ?

+     *  Returns true fi the image will be drawn as a mask, with no intrinsic color of its own.
+     */
+    bool isAlphaOnly() const;
     bool isOpaque() const { return SkAlphaTypeIsOpaque(this->alphaType()); }
 
     /**
      * Extracts YUV planes from the SkImage and stores them in client-provided memory. The sizes
      * planes and rowBytes arrays are ordered [y, u, v].
      */
     bool readYUV8Planes(const SkISize[3], void* const planes[3], const size_t rowBytes[3],
                         SkYUVColorSpace) const;
 
     sk_sp<SkShader> makeShader(SkShader::TileMode, SkShader::TileMode,
@@ skipping 292 matching lines @@
                                                 SkBudgeted, SkSourceGammaTreatment);
 
     const int       fWidth;
     const int       fHeight;
     const uint32_t  fUniqueID;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif