Refactor GrGLUniformManager::UniformHandle to initialize itself by default

src/effects/SkMorphologyImageFilter.cpp

Index: src/effects/SkMorphologyImageFilter.cpp
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index fb8fd00081d2e1b407c98d89d7a6d005b819c93f..a7a6bf14f4c30c4d62fde8ed8b8e4237a42c4e3b 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -312,7 +312,6 @@ private:
 GrGLMorphologyEffect::GrGLMorphologyEffect(const GrBackendEffectFactory& factory,
                                            const GrDrawEffect& drawEffect)
     : INHERITED(factory)
-    , fImageIncrementUni(GrGLUniformManager::kInvalidUniformHandle)
     , fEffectMatrix(drawEffect.castEffect<GrMorphologyEffect>().coordsType()) {
     const GrMorphologyEffect& m = drawEffect.castEffect<GrMorphologyEffect>();
     fRadius = m.radius();