Add desired width & height to drawContext (as opposed to using the width & height of the RT)

src/effects/SkGpuBlurUtils.cpp

Index: src/effects/SkGpuBlurUtils.cpp
diff --git a/src/effects/SkGpuBlurUtils.cpp b/src/effects/SkGpuBlurUtils.cpp
index f0f684dc2d73a045757b7a7a28f4fbaac4d475a4..e192b54b289d1b995703c9667c780dff2fe43b29 100644
--- a/src/effects/SkGpuBlurUtils.cpp
+++ b/src/effects/SkGpuBlurUtils.cpp
@@ -355,7 +355,8 @@ sk_sp<GrDrawContext> GaussianBlur(GrContext* context,
         srcDrawContext->clear(&clearRect, 0x0, false);
 
         SkMatrix matrix;
-        matrix.setIDiv(srcDrawContext->width(), srcDrawContext->height());
+        matrix.setIDiv(srcDrawContext->accessRenderTarget()->width(),
+                       srcDrawContext->accessRenderTarget()->height());
 
         GrPaint paint;
         paint.setGammaCorrect(gammaCorrect);