Re-add canvas flag check to ComputeWebPreferences

The flag was accidentally deleted in the RenderViewHost->WebContents
move. See https://chromium-review.googlesource.com/c/chromium/src/+/2266917/11/content/browser/renderer_host/render_view_host_impl.cc

Bug: 1085003.
Change-Id: Ifdfa90eb02117c5a599ab12bc5b2375e966c704c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2329951
Commit-Queue: Rakina Zata Amni <rakina@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793235}

content/browser/web_contents/web_contents_impl.cc

@@ -2179,7 +2179,8 @@ const WebPreferences WebContentsImpl::ComputeWebPreferences() {
   prefs.accelerated_2d_canvas_enabled =
       !command_line.HasSwitch(switches::kDisableAccelerated2dCanvas);
   prefs.new_canvas_2d_api_enabled =
-      command_line.HasSwitch(switches::kEnableNewCanvas2DAPI);
+      command_line.HasSwitch(switches::kEnableNewCanvas2DAPI) ||
+      base::FeatureList::IsEnabled(features::kEnableNewCanvas2DAPI);
   prefs.antialiased_2d_canvas_disabled =
       command_line.HasSwitch(switches::kDisable2dCanvasAntialiasing);
   prefs.antialiased_clips_2d_canvas_enabled =