converted ConstColorProcessor to SkSL

Bug: skia:
Change-Id: Ic3b18f82c1ab940637fb26dec1cf376dd859b35d
Reviewed-on: https://skia-review.googlesource.com/73720
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/src/gpu/effects/GrCircleEffect.cpp b/src/gpu/effects/GrCircleEffect.cpp
index d3eecb7..3bd2138 100644
--- a/src/gpu/effects/GrCircleEffect.cpp
+++ b/src/gpu/effects/GrCircleEffect.cpp
@@ -75,8 +75,8 @@
             prevRadius = radius;
         }
     }
-    SkPoint prevCenter;
-    float prevRadius;
+    SkPoint prevCenter = half2(0);
+    float prevRadius = 0;
     UniformHandle fCircleVar;
 };
 GrGLSLFragmentProcessor* GrCircleEffect::onCreateGLSLInstance() const {