[inert] Track inertness in ComputedStyle

Both Gecko and WebKit implement inertness based on CSS primitives like
forcing 'pointer-events: none' at used value time, instead of using
a magical hit testing retargeting for inert.

And in whatwg/html#5650, the CSSWG resolved
that this is the right approach.

Then rather than tracking inertness using Node::IsInert, it will just be
simpler to use ComputedStyle::IsInert. This patch implements that.

There are some differences, like nodes in a 'display: none' subtree
won't have a ComputedStyle so we can't really tell if they are inert,
but in practice this doesn't matter since they are not rendered.

Bug: 692360

TEST=StyleResolverTest.IsInertWithAttributeAndDialog
TEST=StyleResolverTest.IsInertWithDialogs
TEST=StyleResolverTest.IsInertWithFullscreen
TEST=StyleResolverTest.IsInertWithFrameAndFullscreen
TEST=StyleResolverTest.IsInertWithBackdrop

Change-Id: I4f8c87ea2fbc17f57290edaf185cdff4aebb7e58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3263937
Reviewed-by: Rune Lillesveen <[email protected]>
Commit-Queue: Oriol Brufau <[email protected]>
Cr-Commit-Position: refs/heads/main@{#941651}
NOKEYCHECK=True
GitOrigin-RevId: ab14f17b660d05dc15925fea64f3cfd92c6f1ed1

blink/renderer/core/css/resolver/style_adjuster.cc

@@ -44,9 +44,11 @@
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/frame/settings.h"
 #include "third_party/blink/renderer/core/frame/web_feature.h"
+#include "third_party/blink/renderer/core/fullscreen/fullscreen.h"
 #include "third_party/blink/renderer/core/html/forms/html_input_element.h"
 #include "third_party/blink/renderer/core/html/forms/html_text_area_element.h"
 #include "third_party/blink/renderer/core/html/html_body_element.h"
+#include "third_party/blink/renderer/core/html/html_dialog_element.h"
 #include "third_party/blink/renderer/core/html/html_iframe_element.h"
 #include "third_party/blink/renderer/core/html/html_image_element.h"
 #include "third_party/blink/renderer/core/html/html_plugin_element.h"
@@ -677,6 +679,31 @@ static void AdjustStateForContentVisibility(ComputedStyle& style,
   context->AdjustElementStyle(&style);
 }
 
+static void AdjustStyleForInert(ComputedStyle& style, Element* element) {
+  if (!element || style.IsForcedInert())
+    return;
+
+  if (RuntimeEnabledFeatures::InertAttributeEnabled() &&
+      element->FastHasAttribute(html_names::kInertAttr) &&
+      element->IsHTMLElement()) {
+    style.SetIsForcedInert();
+    return;
+  }
+
+  Document& document = element->GetDocument();
+  const Element* modal_element = document.ActiveModalDialog();
+  if (!modal_element)
+    modal_element = Fullscreen::FullscreenElementFrom(document);
+  if (modal_element == element) {
+    style.SetIsInert(false);
+    return;
+  }
+  if (modal_element && element == document.documentElement()) {
+    style.SetIsInert(true);
+    return;
+  }
+}
+
 void StyleAdjuster::AdjustForForcedColorsMode(ComputedStyle& style) {
   if (!style.InForcedColorsMode() ||
       style.ForcedColorAdjust() != EForcedColorAdjust::kAuto)
@@ -818,6 +845,8 @@ void StyleAdjuster::AdjustComputedStyle(StyleResolverState& state,
   // Let the theme also have a crack at adjusting the style.
   LayoutTheme::GetTheme().AdjustStyle(element, style);
 
+  AdjustStyleForInert(style, element);
+
   AdjustStyleForEditing(style);
 
   bool is_svg_root = false;

blink/renderer/core/css/resolver/style_resolver.cc

@@ -1215,6 +1215,9 @@ scoped_refptr<ComputedStyle> StyleResolver::InitialStyleForElement() const {
   if (initial_data)
     initial_style->SetInitialData(std::move(initial_data));
 
+  if (frame && frame->IsInert())
+    initial_style->SetIsForcedInert();
+
   return initial_style;
 }