Add functions for inspecting SkShader.

include/core/SkShader.h

Index: include/core/SkShader.h
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index ce5f00387339158267df4f6ee3f90b6a32f95b5e..bc83c320cd2c9703659367ee88ae058a27a00b65 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -17,6 +17,7 @@
 
 class SkPath;
 class SkPicture;
+class SkXfermode;
 class GrContext;
 class GrEffectRef;
 
@@ -356,6 +357,20 @@ public:
     virtual GradientType asAGradient(GradientInfo* info) const;
 
     /**
+     *  If the shader subclass is composed of two shaders, return true, and if rec is not NULL,
+     *  fill it out with info about the shader.

[reed1, 2014/05/13 18:00:24]

? What is the ownership-rule for the returned pointers? 

I presume the answer is that they are bare-pointers, and that if the caller
wants to retain them, he needs to call ref. But no matter what we should
document this (now or in a later CL).

[scroggo, 2014/05/14 13:51:26]

Uploaded https://codereview.chromium.org/288713002

+     */
+
+    struct ComposeRec {
+        const SkShader*     fShaderA;
+        const SkShader*     fShaderB;
+        const SkXfermode*   fMode;
+    };
+
+    virtual bool asACompose(ComposeRec* rec) const { return false; }
+
+
+    /**
      *  If the shader subclass has a GrEffect implementation, this resturns the effect to install.
      *  The incoming color to the effect has r=g=b=a all extracted from the SkPaint's alpha.
      *  The output color should be the computed SkShader premul color modulated by the incoming
@@ -365,6 +380,14 @@ public:
     virtual GrEffectRef* asNewEffect(GrContext* context, const SkPaint& paint,
                                      const SkMatrix* localMatrixOrNull) const;
 
+#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
+    /**
+     *  If the shader is a custom shader which has data the caller might want, call this function
+     *  to get that data.
+     */
+    virtual bool asACustomShader(void** customData) const { return false; }
+#endif
+
     //////////////////////////////////////////////////////////////////////////
     //  Factory methods for stock shaders