Implement GPU occluded blur mask filter

include/effects/SkBlurMaskFilter.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBlurMaskFilter_DEFINED
 #define SkBlurMaskFilter_DEFINED
 
@@ skipping 14 matching lines @@
         kNone_BlurFlag = 0x00,
         /** The blur layer's radius is not affected by transforms */
         kIgnoreTransform_BlurFlag   = 0x01,
         /** Use a smother, higher qulity blur algorithm */
         kHighQuality_BlurFlag       = 0x02,
         /** mask for all blur flags */
         kAll_BlurFlag = 0x03
     };
 
     /** Create a blur maskfilter.
-     *  @param style    The SkBlurStyle to use
-     *  @param sigma    Standard deviation of the Gaussian blur to apply. Must be > 0.
-     *  @param flags    Flags to use - defaults to none
+     *  @param style     The SkBlurStyle to use
+     *  @param sigma     Standard deviation of the Gaussian blur to apply. Must be > 0.
+     *  @param occluder  The rect for which no pixels need be drawn (b.c. it will be overdrawn
+     *                   with some opaque object. This is just a hint which backends are free to
+     *                   ignore.
+     *  @param flags     Flags to use - defaults to none
      *  @return The new blur maskfilter
      */
     static sk_sp<SkMaskFilter> Make(SkBlurStyle style, SkScalar sigma,
-                                    uint32_t flags = kNone_BlurFlag);
+                                    const SkRect& occluder, uint32_t flags = kNone_BlurFlag);
+
+    static sk_sp<SkMaskFilter> Make(SkBlurStyle style, SkScalar sigma,
+                                    uint32_t flags = kNone_BlurFlag) {
+        return Make(style, sigma, SkRect::MakeEmpty(), flags);
+    }
 
     /** Create an emboss maskfilter
         @param blurSigma    standard deviation of the Gaussian blur to apply
                             before applying lighting (e.g. 3)
         @param direction    array of 3 scalars [x, y, z] specifying the direction of the light source
         @param ambient      0...1 amount of ambient light
         @param specular     coefficient for specular highlights (e.g. 8)
         @return the emboss maskfilter
     */
     static sk_sp<SkMaskFilter> MakeEmboss(SkScalar blurSigma, const SkScalar direction[3],
@@ skipping 23 matching lines @@
                                           int* numYs);
 
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 
 private:
     SkBlurMaskFilter(); // can't be instantiated
 };
 
 #endif