Remove nullcheck from RenderWidget::SynchronizeVisualProperties

Sync visual properties is only called in response to an IPC. The close
IPC drops the IPC route before removing the WebWidget so IPCs can't
arrive that would SynchronizeVisualProperties() after the WebWidget is
gone.

The one exception is the screen metrics emulator which can call it from
its destructor, but it is also destroyed in CloseWebWidget() before the
WebWidget is destroyed precisely to avoid these sorts of things (with
a TODO about how to make that more clear..).

R=avi@chromium.org

Change-Id: I0621f4e3f4a708dd209b996129b9e17a765d6296
Bug: 912193
Reviewed-on: https://chromium-review.googlesource.com/c/1427881Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625219}

content/renderer/render_widget.cc

@@ -1402,10 +1402,6 @@ void RenderWidget::SynchronizeVisualProperties(const VisualProperties& params) {
   if (render_thread)
     render_thread->SetRenderingColorSpace(params.screen_info.color_space);
 
-  // Ignore this during shutdown.
-  if (!GetWebWidget())
-    return;
-
   // Only propagate the external PSF to non-main-frames.
   if (!delegate())
     layer_tree_view_->SetExternalPageScaleFactor(params.page_scale_factor);