Registry-based unit test for custom effects

Review URL: http://codereview.appspot.com/6447085/



git-svn-id: http://skia.googlecode.com/svn/trunk@4946 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLProgram.h b/src/gpu/gl/GrGLProgram.h
index 62c70e5..989b7c6 100644
--- a/src/gpu/gl/GrGLProgram.h
+++ b/src/gpu/gl/GrGLProgram.h
@@ -259,8 +259,10 @@
 
     void genUniformCoverage(GrGLShaderBuilder* segments, SkString* inOutCoverage);
 
-    // generates code to compute coverage based on edge AA.
-    void genEdgeCoverage(SkString* coverageVar, GrGLShaderBuilder* builder) const;
+    // generates code to compute coverage based on edge AA. Returns true if edge coverage was
+    // inserted in which case coverageVar will be updated to refer to a scalar. Otherwise,
+    // coverageVar is set to an empty string.
+    bool genEdgeCoverage(SkString* coverageVar, GrGLShaderBuilder* builder) const;
 
     // Creates a GL program ID, binds shader attributes to GL vertex attrs, and links the program
     bool bindOutputsAttribsAndLinkProgram(SkString texCoordAttrNames[GrDrawState::kMaxTexCoords],