content-visibility: Fix DCHECK in graphics layer update.

This patch ensures that the DCHECK doesn't trigger when checking that
the dirty bits have been cleared on the graphics layer updater.

This follows the same pattern as the update, skipping checks on locked
children.

R=chrishtr@chromium.org

Change-Id: I81ae6a6ca4279472dd3433db9f23b2295fd52ddb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2452849Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814364}

third_party/blink/renderer/core/display_lock/display_lock_context_test.cc

@@ -26,6 +26,7 @@
 #include "third_party/blink/renderer/core/frame/web_local_frame_impl.h"
 #include "third_party/blink/renderer/core/geometry/dom_rect.h"
 #include "third_party/blink/renderer/core/html/html_template_element.h"
+#include "third_party/blink/renderer/core/paint/compositing/composited_layer_mapping.h"
 #include "third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.h"
 #include "third_party/blink/renderer/core/paint/paint_layer.h"
 #include "third_party/blink/renderer/core/style/computed_style.h"
@@ -2970,4 +2971,52 @@ TEST_F(DisplayLockContextLegacyRenderingTest,
   UpdateAllLifecyclePhasesForTest();
 }
 
+TEST_F(DisplayLockContextTest, GraphicsLayerBitsNotCheckedInLockedSubtree) {
+  ResizeAndFocus();
+  GetDocument().GetSettings()->SetPreferCompositingToLCDTextEnabled(true);
+
+  SetHtmlInnerHTML(R"HTML(
+    <style>
+    div {
+      width: 100px;
+      height: 100px;
+      contain: style layout;
+      will-change: transform;
+    }
+    .locked {
+      content-visibility: hidden;
+    }
+    </style>
+    <div id=container>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+  )HTML");
+
+  // Check if the result is correct if we update the contents.
+  auto* container = GetDocument().getElementById("container");
+  auto* target = GetDocument().getElementById("target");
+  auto* target_box = ToLayoutBoxModelObject(target->GetLayoutObject());
+  ASSERT_TRUE(target_box);
+  EXPECT_TRUE(target_box->Layer());
+  EXPECT_TRUE(target_box->HasSelfPaintingLayer());
+  auto* target_layer = target_box->Layer();
+  ASSERT_TRUE(target_layer->HasCompositedLayerMapping());
+
+  container->classList().Add("locked");
+  target_layer->GetCompositedLayerMapping()->SetNeedsGraphicsLayerUpdate(
+      kGraphicsLayerUpdateLocal);
+  // This should not DCHECK.
+  UpdateAllLifecyclePhasesForTest();
+
+  EXPECT_TRUE(
+      target_layer->GetCompositedLayerMapping()->NeedsGraphicsLayerUpdate());
+
+  container->classList().Remove("locked");
+  UpdateAllLifecyclePhasesForTest();
+
+  EXPECT_FALSE(
+      target_layer->GetCompositedLayerMapping()->NeedsGraphicsLayerUpdate());
+}
 }  // namespace blink

third_party/blink/renderer/core/paint/compositing/graphics_layer_updater.cc

@@ -175,8 +175,11 @@ void GraphicsLayerUpdater::AssertNeedsToUpdateGraphicsLayerBitsCleared(
         ->AssertNeedsToUpdateGraphicsLayerBitsCleared();
   }
 
-  for (PaintLayer* child = layer.FirstChild(); child;
-       child = child->NextSibling())
+  PaintLayer* first_child =
+      layer.GetLayoutObject().ChildPrePaintBlockedByDisplayLock()
+          ? nullptr
+          : layer.FirstChild();
+  for (PaintLayer* child = first_child; child; child = child->NextSibling())
     AssertNeedsToUpdateGraphicsLayerBitsCleared(*child);
 }