Remove uses of skia::GetWritablePixels(PaintCanvas)

cc/paint/paint_canvas.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/paint/paint_canvas.h"
 
 namespace cc {
 
 PaintCanvasPassThrough::PaintCanvasPassThrough(SkCanvas* canvas)
     : SkNWayCanvas(canvas->getBaseLayerSize().width(),
                    canvas->getBaseLayerSize().height()) {
   SkIRect raster_bounds;
   canvas->getDeviceClipBounds(&raster_bounds);
   clipRect(SkRect::MakeFromIRect(raster_bounds));
   setMatrix(canvas->getTotalMatrix());
   addCanvas(canvas);
 }
 
 PaintCanvasPassThrough::PaintCanvasPassThrough(int width, int height)
     : SkNWayCanvas(width, height) {}
 
 PaintCanvasPassThrough::~PaintCanvasPassThrough() = default;
 
+bool ToPixmap(PaintCanvas* canvas, SkPixmap* output) {
+  SkImageInfo info;
+  size_t row_bytes;
+  void* pixels = canvas->accessTopLayerPixels(&info, &row_bytes);
+  if (!pixels) {
+    output->reset();
+    return false;
+  }
+
+  output->reset(info, pixels, row_bytes);
+  return true;
+}
+
 }  // namespace cc