Have GrRectBlurEffect use Linear filtering (rather than Nearest Neighbor)

Review URL: https://codereview.chromium.org/1378023004
diff --git a/src/effects/SkBlurMaskFilter.cpp b/src/effects/SkBlurMaskFilter.cpp
index 58242b7..8908fa9 100644
--- a/src/effects/SkBlurMaskFilter.cpp
+++ b/src/effects/SkBlurMaskFilter.cpp
@@ -769,7 +769,7 @@
 GrRectBlurEffect::GrRectBlurEffect(const SkRect& rect, float sigma, GrTexture *blurProfile)
     : fRect(rect)
     , fSigma(sigma)
-    , fBlurProfileAccess(blurProfile) {
+    , fBlurProfileAccess(blurProfile, GrTextureParams::kBilerp_FilterMode) {
     this->initClassID<GrRectBlurEffect>();
     this->addTextureAccess(&fBlurProfileAccess);
     this->setWillReadFragmentPosition();