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

src/core/SkSpecialSurface.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file
  */
 
 #include "SkCanvas.h"
 #include "SkSpecialImage.h"
 #include "SkSpecialSurface.h"
@@ skipping 97 matching lines @@
     return sk_make_sp<SkSpecialSurface_Raster>(pr, subset, props);
 }
 
 #if SK_SUPPORT_GPU
 ///////////////////////////////////////////////////////////////////////////////
 #include "GrContext.h"
 #include "SkGpuDevice.h"
 
 class SkSpecialSurface_Gpu : public SkSpecialSurface_Base {
 public:
-    SkSpecialSurface_Gpu(sk_sp<GrDrawContext> drawContext,
-                         int width, int height,
-                         const SkIRect& subset)
+    SkSpecialSurface_Gpu(sk_sp<GrDrawContext> drawContext, const SkIRect& subset)
         : INHERITED(subset, &drawContext->surfaceProps())
         , fDrawContext(std::move(drawContext)) {
 
-        sk_sp<SkBaseDevice> device(SkGpuDevice::Make(fDrawContext, width, height,
+        sk_sp<SkBaseDevice> device(SkGpuDevice::Make(fDrawContext,
                                                      SkGpuDevice::kUninit_InitContents));
         if (!device) {
             return;
         }
 
         fCanvas.reset(new SkCanvas(device.get()));
         fCanvas->clipRect(SkRect::Make(subset));
 #ifdef SK_IS_BOT
         fCanvas->clear(SK_ColorRED);  // catch any imageFilter sloppiness
 #endif
@@ skipping 24 matching lines @@
     }
 
     sk_sp<GrDrawContext> drawContext(context->newDrawContext(SkBackingFit::kApprox,
                                                              width, height, config));
     if (!drawContext) {
         return nullptr;
     }
 
     const SkIRect subset = SkIRect::MakeWH(width, height);
 
-    return sk_make_sp<SkSpecialSurface_Gpu>(std::move(drawContext), width, height, subset);
+    return sk_make_sp<SkSpecialSurface_Gpu>(std::move(drawContext), subset);
 }
 
 #endif