Only use msaa target for blur mask when doAA is true

src/gpu/SkGpuDevice.cpp

Index: src/gpu/SkGpuDevice.cpp
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index 22968a781305a82ef59049d7a22b52ed5838ec49..f6ac9638ad28b3d080946537fb7543381a984173 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -636,7 +636,7 @@ bool create_mask_GPU(GrContext* context,
     desc.fFlags = kRenderTarget_GrTextureFlagBit;
     desc.fWidth = SkScalarCeilToInt(maskRect.width());
     desc.fHeight = SkScalarCeilToInt(maskRect.height());
-    desc.fSampleCnt = SampleCnt;
+    desc.fSampleCnt = doAA ? SampleCnt : 0;
     // We actually only need A8, but it often isn't supported as a
     // render target so default to RGBA_8888
     desc.fConfig = kRGBA_8888_GrPixelConfig;