cleanup and adds docs

atom/browser/native_window.cc

@@ -207,6 +207,7 @@ void NativeWindow::InitFromOptions(const mate::Dictionary& options) {
 void NativeWindow::SetSize(const gfx::Size& size, bool animate) {
   SetBounds(gfx::Rect(GetPosition(), size), animate);
 
+  // In offscreen mode call RenderWidgetHostView's SetSize explicitly
   const auto view = web_contents()->GetRenderWidgetHostView();
   if (view) {
     auto old_size = view->GetViewBounds().size();

atom/browser/osr/osr_output_device.cc

@@ -24,8 +24,6 @@ void OffScreenOutputDevice::Resize(
     const gfx::Size& pixel_size, float scale_factor) {
   scale_factor_ = scale_factor;
 
-  printf("OffScreenOutputDevice::Resize\n");
-
   if (viewport_pixel_size_ == pixel_size) return;
   viewport_pixel_size_ = pixel_size;
 

atom/browser/osr/osr_render_widget_host_view.cc

@@ -891,7 +891,6 @@ void OffScreenRenderWidgetHostView::SetupFrameRate(bool force) {
 void OffScreenRenderWidgetHostView::Invalidate() {
   const gfx::Rect& bounds_in_pixels = GetViewBounds();
 
-  printf("Invalidate\n");
   if (software_output_device_) {
     software_output_device_->OnPaint(bounds_in_pixels);
   } else if (copy_frame_generator_.get()) {

docs/api/web-contents.md

@@ -1146,6 +1146,11 @@ Only values between 1 and 60 are accepted.
 
 If *offscreen rendering* is enabled returns the current frame rate.
 
+#### `contents.invalidate()`
+
+If *offscreen rendering* is enabled invalidates the frame and generates a new
+one through the `'paint'` event.
+
 ### Instance Properties
 
 #### `contents.id`