implement isABitmap for imageshader, return localmatrix for bitmap's impl

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 69037d95f663bc34d597a2014754a0859c3cfb78..c442fae4fd7d0ca45e06086b6ef480c066bd1e23 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -18,6 +18,7 @@
 
 class SkColorFilter;
 class SkColorSpace;
+class SkImage;
 class SkPath;
 class SkPicture;
 class SkXfermode;
@@ -242,6 +243,18 @@ public:
     }
 
     /**
+     *  Iff this shader is backed by a single SkImage, return its ptr (the caller must ref this
+     *  if they want to keep it longer than the lifetime of the shader). If not, return nullptr.
+     */
+    SkImage* isAImage(SkMatrix* localMatrix, TileMode xy[2]) const {
+        return this->onIsAImage(localMatrix, xy);
+    }
+
+    bool isAImage() const {
+        return this->isAImage(nullptr, nullptr) != nullptr;
+    }
+
+    /**
      *  If the shader subclass can be represented as a gradient, asAGradient
      *  returns the matching GradientType enum (or kNone_GradientType if it
      *  cannot). Also, if info is not null, asAGradient populates info with
@@ -512,6 +525,10 @@ protected:
         return false;
     }
 
+    virtual SkImage* onIsAImage(SkMatrix*, TileMode[2]) const {
+        return nullptr;
+    }
+
 private:
     // This is essentially const, but not officially so it can be modified in
     // constructors.