Sky shouldn't crash on device rotate

sky/viewer/document_view.cc

Index: sky/viewer/document_view.cc
diff --git a/sky/viewer/document_view.cc b/sky/viewer/document_view.cc
index cf48567326bc26586232d47481fbbeba49e07d77..ab1516d0d5345835eae0d6bb1e2da12646fe0510 100644
--- a/sky/viewer/document_view.cc
+++ b/sky/viewer/document_view.cc
@@ -270,8 +270,9 @@ void DocumentView::OnViewBoundsChanged(mojo::View* view,
                                        const mojo::Rect& old_bounds,
                                        const mojo::Rect& new_bounds) {
   DCHECK_EQ(view, root_);
-  gfx::Size size = new_bounds.To<gfx::Rect>().size();
-  web_view_->resize(size);
+  float device_pixel_ratio = GetDevicePixelRatio();
+  web_view_->resize(blink::WebSize(new_bounds.width / device_pixel_ratio,
+                                   new_bounds.height / device_pixel_ratio));
 }
 
 void DocumentView::OnViewFocusChanged(mojo::View* gained_focus,