Ensure compositing update when a canvas is connected to an offscreen canvas

Bug: 1005868
Change-Id: Ice99c87d4eff6306baa14fbfe91e859295169786
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819563
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699143}

third_party/blink/renderer/core/BUILD.gn

@@ -1222,6 +1222,7 @@ jumbo_source_set("unit_tests") {
     "html/anchor_element_metrics_test.cc",
     "html/canvas/canvas_async_blob_creator_test.cc",
     "html/canvas/canvas_font_cache_test.cc",
+    "html/canvas/html_canvas_element_test.cc",
     "html/canvas/image_data_test.cc",
     "html/custom/custom_element_definition_test.cc",
     "html/custom/custom_element_descriptor_test.cc",

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

@@ -1393,6 +1393,8 @@ void HTMLCanvasElement::CreateLayer() {
         base::DoNothing());
     // Creates a placeholder layer first before Surface is created.
     surface_layer_bridge_->CreateSolidColorLayer();
+    // This may cause the canvas to be composited.
+    SetNeedsCompositingUpdate();
   }
 }
 

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

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "third_party/blink/renderer/core/html/canvas/html_canvas_element.h"
+
+#include "third_party/blink/renderer/core/paint/paint_layer.h"
+#include "third_party/blink/renderer/core/testing/core_unit_test_helper.h"
+
+namespace blink {
+
+using HTMLCanvasElementTest = RenderingTest;
+
+TEST_F(HTMLCanvasElementTest, CreateLayerUpdatesCompositing) {
+  // Enable script so that the canvas will create a LayoutHTMLCanvas.
+  GetDocument().GetSettings()->SetScriptEnabled(true);
+
+  SetBodyInnerHTML("<canvas id='canvas'></canvas>");
+  auto* canvas = ToHTMLCanvasElement(GetDocument().getElementById("canvas"));
+  auto* layer = ToLayoutBoxModelObject(canvas->GetLayoutObject())->Layer();
+  ASSERT_TRUE(layer);
+  EXPECT_EQ(CompositingReason::kNone, layer->DirectCompositingReasons());
+
+  EXPECT_FALSE(layer->NeedsCompositingInputsUpdate());
+  canvas->CreateLayer();
+  EXPECT_TRUE(layer->NeedsCompositingInputsUpdate());
+  UpdateAllLifecyclePhasesForTest();
+  ASSERT_EQ(layer, ToLayoutBoxModelObject(canvas->GetLayoutObject())->Layer());
+  EXPECT_EQ(CompositingReason::kCanvas, layer->DirectCompositingReasons());
+}
+
+}  // namespace blink