fUsesLocalCoords is updated in the parent when a child proc is registered.

src/gpu/GrProcessor.cpp

Index: src/gpu/GrProcessor.cpp
diff --git a/src/gpu/GrProcessor.cpp b/src/gpu/GrProcessor.cpp
index 6716ab1d12d6b2030f21fed850c34d83c6a0c0e0..db1e2d9f6198a0103c08728a8326b6dbf9ef5df3 100644
--- a/src/gpu/GrProcessor.cpp
+++ b/src/gpu/GrProcessor.cpp
@@ -205,6 +205,10 @@ int GrFragmentProcessor::registerChildProcessor(const GrFragmentProcessor* child
         this->setWillReadFragmentPosition();
     }
 
+    if (child->usesLocalCoords()) {
+        fUsesLocalCoords = true;
+    }
+
     return index;
 }