GrFP can express distance vector field req., program builder declares variable for it

src/gpu/glsl/GrGLSLProgramBuilder.cpp

Index: src/gpu/glsl/GrGLSLProgramBuilder.cpp
diff --git a/src/gpu/glsl/GrGLSLProgramBuilder.cpp b/src/gpu/glsl/GrGLSLProgramBuilder.cpp
index 31d1de29b3ba89da5a7b22a0fc2b716e9337b51a..f606768fb6a10b516bea1d32354cf832f2163711 100644
--- a/src/gpu/glsl/GrGLSLProgramBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLProgramBuilder.cpp
@@ -87,6 +87,11 @@ void GrGLSLProgramBuilder::emitAndInstallPrimProc(const GrPrimitiveProcessor& pr
     this->nameExpression(outputColor, "outputColor");
     this->nameExpression(outputCoverage, "outputCoverage");
 
+    if (this->fPipeline.usesDistanceVectorField() && proc.implementsDistanceVector()) {
+        fFS.codeAppend( "// Un-normalized vector to the closed geometric edge (in source space)\n");
+        fFS.codeAppendf("vec2 %s = vec2(0.0, 0.0);", fFS.distanceVectorName());
+    }
+
     // Enclose custom code in a block to avoid namespace conflicts
     SkString openBrace;
     openBrace.printf("{ // Stage %d, %s\n", fStageIndex, proc.name());
@@ -161,7 +166,9 @@ void GrGLSLProgramBuilder::emitAndInstallFragProc(const GrFragmentProcessor& fp,
                                            input.isOnes() ? nullptr : input.c_str(),
                                            fOutCoords[index],
                                            texSamplers.begin(),
-                                           bufferSamplers.begin());
+                                           bufferSamplers.begin(),
+                                           this->primitiveProcessor().implementsDistanceVector());
+
     fragProc->emitCode(args);
 
     // We have to check that effects and the code they emit are consistent, ie if an effect