No handling of frame-less canvas element for OffscreenCanvas

As this use case is too small to be worth the effort, we archive this task and
modify comments.

TBR=junov@chromium.org

Bug: 683172
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ic1f55ed6c5a8b7ae074f7e03b8c07fa1bc7a4815
Reviewed-on: https://chromium-review.googlesource.com/1055814
Commit-Queue: Olivia Lai <xlai@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558007}

third_party/WebKit/LayoutTests/fast/canvas/OffscreenCanvas-commit-frameless-doc.html

@@ -7,8 +7,6 @@
 // Since the document is invisible, the resultant image should be
 // not visible too. But users must be able to draw to the OffscreenCanvas
 // and do canvas-operations on the frameless placeholder canvas.
-// TODO(crbug.com/683172): Modify this test after handling for
-// frameless canvas is done.
 function createFramelessCanvas() {
   var framelessDoc = document.implementation.createHTMLDocument("frameless");
   var canvas = framelessDoc.createElement("canvas");

third_party/blink/renderer/core/html/canvas/html_canvas_element.cc

@@ -1465,9 +1465,7 @@ void HTMLCanvasElement::CreateLayer() {
   DCHECK(!surface_layer_bridge_);
   LocalFrame* frame = GetDocument().GetFrame();
   WebLayerTreeView* layer_tree_view = nullptr;
-  // TODO(xlai): Ensure OffscreenCanvas commit() is still functional when a
-  // frame-less HTML canvas's document is reparenting under another frame.
-  // See crbug.com/683172.
+  // We do not design transferControlToOffscreen() for frame-less HTML canvas.
   if (frame) {
     layer_tree_view =
         frame->GetPage()->GetChromeClient().GetWebLayerTreeView(frame);

third_party/blink/renderer/platform/graphics/surface_layer_bridge.cc

@@ -33,9 +33,6 @@ SurfaceLayerBridge::SurfaceLayerBridge(WebLayerTreeView* layer_tree_view,
   mojom::blink::EmbeddedFrameSinkProviderPtr provider;
   Platform::Current()->GetInterfaceProvider()->GetInterface(
       mojo::MakeRequest(&provider));
-  // TODO(xlai): Ensure OffscreenCanvas commit() is still functional when a
-  // frame-less HTML canvas's document is reparenting under another frame.
-  // See crbug.com/683172.
   blink::mojom::blink::EmbeddedFrameSinkClientPtr client;
   binding_.Bind(mojo::MakeRequest(&client));
   provider->RegisterEmbeddedFrameSink(parent_frame_sink_id_, frame_sink_id_,