More prep work in Gr for landing AA hairline renderer.

Review URL: http://codereview.appspot.com/4944045



git-svn-id: http://skia.googlecode.com/svn/trunk@2164 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index 105c456..a8d1942 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -694,7 +694,8 @@
 #endif
     SkMaskFilter::BlurInfo info;
     SkMaskFilter::BlurType blurType = filter->asABlur(&info);
-    if (SkMaskFilter::kNone_BlurType == blurType) {
+    if (SkMaskFilter::kNone_BlurType == blurType ||
+        !context->supportsShaders()) {
         return false;
     }
     SkScalar radius = info.fIgnoreTransform ? info.fRadius