Unify invalidation code paths for font-face rule changes and font loading

Currently, there are two different invalidation code paths for font-face
related changes:

1. Via FontSelector::FontFaceInvalidated(). This is called when:
- The loading status of a font changes
- A FontFace is changed via the JavaScript API

This code path also allows partial style invalidation when the feature
CSSReducedFontLoadingInvalidations is enabled; Otherwise, it marks the
full document's style as dirty.

2. Via StyleEngine::InvalidateForRuleSetChanges(). This is called when
StyleEngine identifies changes in the active @font-face rules. It marks
the full document's style as dirty.

This patch makes (2) to also use FontSelector::FontFaceInvalidated() to
update style and layout, instead of directly marking full document style
dirty. As a result:

- When the feature is enabled, @font-face rule changes don't need full
  document style recalc

- We no longer need to compare FontSelector versions in style diff. This
  is required by partial layout recalc for font loading

- There is no essential behavioral change when the feature is disabled,
  since in that case both code paths mark style dirty on the full doc

Note: there's also a renaming to certain variables & functions to make
code more readable, since what they actually rebuild is FontFaceCache
instead of FontCache.

Bug: 441925
Change-Id: I5207e99fdb7e610bcdedc4c7b3615b0c13b69c6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147687Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759124}

third_party/blink/renderer/core/css/active_style_sheets_test.cc

@@ -470,8 +470,12 @@ TEST_F(ApplyRulesetsTest, AddFontFaceRuleToDocument) {
   GetStyleEngine().ApplyRuleSetChanges(GetDocument(), ActiveStyleSheetVector(),
                                        new_style_sheets);
 
-  EXPECT_EQ(kSubtreeStyleChange,
-            GetDocument().documentElement()->GetStyleChangeType());
+  StyleChangeType expected =
+      RuntimeEnabledFeatures::CSSReducedFontLoadingInvalidationsEnabled()
+          ? kNoStyleChange
+          : kSubtreeStyleChange;
+
+  EXPECT_EQ(expected, GetDocument().documentElement()->GetStyleChangeType());
 }
 
 TEST_F(ApplyRulesetsTest, AddFontFaceRuleToShadowTree) {

third_party/blink/renderer/core/css/style_engine.cc

@@ -738,7 +738,7 @@ void StyleEngine::DidDetach() {
   environment_variables_ = nullptr;
 }
 
-bool StyleEngine::ClearFontCacheAndAddUserFonts() {
+bool StyleEngine::ClearFontFaceCacheAndAddUserFonts() {
   bool fonts_changed = false;
 
   if (font_selector_ &&
@@ -1515,29 +1515,18 @@ unsigned GetRuleSetFlags(const HeapHashSet<Member<RuleSet>> rule_sets) {
   return flags;
 }
 
-bool NeedsFullRecalcForRuleSetChanges(TreeScope& tree_scope,
-                                      unsigned changed_rule_flags,
-                                      bool has_rebuilt_font_cache) {
-  if (changed_rule_flags & kFullRecalcRules)
-    return true;
-  if (!tree_scope.RootNode().IsDocumentNode())
-    return false;
-  return (changed_rule_flags & kFontFaceRules) || has_rebuilt_font_cache;
-}
-
 }  // namespace
 
 void StyleEngine::InvalidateForRuleSetChanges(
     TreeScope& tree_scope,
     const HeapHashSet<Member<RuleSet>>& changed_rule_sets,
     unsigned changed_rule_flags,
-    InvalidationScope invalidation_scope,
-    bool has_rebuilt_font_cache) {
+    InvalidationScope invalidation_scope) {
   if (tree_scope.GetDocument().HasPendingForcedStyleRecalc())
     return;
   if (!tree_scope.GetDocument().documentElement())
     return;
-  if (changed_rule_sets.IsEmpty() && !has_rebuilt_font_cache)
+  if (changed_rule_sets.IsEmpty())
     return;
 
   Element& invalidation_root =
@@ -1545,8 +1534,7 @@ void StyleEngine::InvalidateForRuleSetChanges(
   if (invalidation_root.GetStyleChangeType() == kSubtreeStyleChange)
     return;
 
-  if (NeedsFullRecalcForRuleSetChanges(tree_scope, changed_rule_flags,
-                                       has_rebuilt_font_cache)) {
+  if (changed_rule_flags & kFullRecalcRules) {
     invalidation_root.SetNeedsStyleRecalc(
         kSubtreeStyleChange,
         StyleChangeReasonForTracing::Create(
@@ -1581,7 +1569,7 @@ void StyleEngine::ApplyUserRuleSetChanges(
   global_rule_set_->MarkDirty();
 
   unsigned changed_rule_flags = GetRuleSetFlags(changed_rule_sets);
-  bool has_rebuilt_font_cache = false;
+  bool has_rebuilt_font_face_cache = false;
   if (changed_rule_flags & kFontFaceRules) {
     if (ScopedStyleResolver* scoped_resolver =
             GetDocument().GetScopedStyleResolver()) {
@@ -1592,7 +1580,7 @@ void StyleEngine::ApplyUserRuleSetChanges(
       scoped_resolver->SetNeedsAppendAllSheets();
       MarkDocumentDirty();
     } else {
-      has_rebuilt_font_cache = ClearFontCacheAndAddUserFonts();
+      has_rebuilt_font_face_cache = ClearFontFaceCacheAndAddUserFonts();
     }
   }
 
@@ -1608,9 +1596,11 @@ void StyleEngine::ApplyUserRuleSetChanges(
     ScopedStyleResolver::KeyframesRulesAdded(GetDocument());
   }
 
+  if ((changed_rule_flags & kFontFaceRules) || has_rebuilt_font_face_cache)
+    GetFontSelector()->FontFaceInvalidated();
+
   InvalidateForRuleSetChanges(GetDocument(), changed_rule_sets,
-                              changed_rule_flags, kInvalidateAllScopes,
-                              has_rebuilt_font_cache);
+                              changed_rule_flags, kInvalidateAllScopes);
 }
 
 void StyleEngine::ApplyRuleSetChanges(
@@ -1626,12 +1616,12 @@ void StyleEngine::ApplyRuleSetChanges(
 
   unsigned changed_rule_flags = GetRuleSetFlags(changed_rule_sets);
 
-  bool rebuild_font_cache = change == kActiveSheetsChanged &&
-                            (changed_rule_flags & kFontFaceRules) &&
-                            tree_scope.RootNode().IsDocumentNode();
+  bool rebuild_font_face_cache = change == kActiveSheetsChanged &&
+                                 (changed_rule_flags & kFontFaceRules) &&
+                                 tree_scope.RootNode().IsDocumentNode();
   ScopedStyleResolver* scoped_resolver = tree_scope.GetScopedStyleResolver();
   if (scoped_resolver && scoped_resolver->NeedsAppendAllSheets()) {
-    rebuild_font_cache = true;
+    rebuild_font_face_cache = true;
     change = kActiveSheetsChanged;
   }
 
@@ -1658,9 +1648,9 @@ void StyleEngine::ApplyRuleSetChanges(
     }
   }
 
-  bool has_rebuilt_font_cache = false;
-  if (rebuild_font_cache)
-    has_rebuilt_font_cache = ClearFontCacheAndAddUserFonts();
+  bool has_rebuilt_font_face_cache = false;
+  if (rebuild_font_face_cache)
+    has_rebuilt_font_face_cache = ClearFontFaceCacheAndAddUserFonts();
 
   unsigned append_start_index = 0;
   if (scoped_resolver) {
@@ -1682,8 +1672,13 @@ void StyleEngine::ApplyRuleSetChanges(
         append_start_index, new_style_sheets);
   }
 
+  if (tree_scope.RootNode().IsDocumentNode()) {
+    if ((changed_rule_flags & kFontFaceRules) || has_rebuilt_font_face_cache)
+      GetFontSelector()->FontFaceInvalidated();
+  }
+
   InvalidateForRuleSetChanges(tree_scope, changed_rule_sets, changed_rule_flags,
-                              kInvalidateCurrentScope, has_rebuilt_font_cache);
+                              kInvalidateCurrentScope);
 }
 
 void StyleEngine::LoadVisionDeficiencyFilter() {

third_party/blink/renderer/core/css/style_engine.h

@@ -464,8 +464,7 @@ class CORE_EXPORT StyleEngine final : public GarbageCollected<StyleEngine>,
       TreeScope& tree_scope,
       const HeapHashSet<Member<RuleSet>>& changed_rule_sets,
       unsigned changed_rule_flags,
-      InvalidationScope invalidation_scope,
-      bool rebuild_font_cache);
+      InvalidationScope invalidation_scope);
   void InvalidateInitialData();
 
   void UpdateViewport();
@@ -480,7 +479,7 @@ class CORE_EXPORT StyleEngine final : public GarbageCollected<StyleEngine>,
   void UpdateStyleSheetList(TreeScope&);
 
   // Returns true if any @font-face rules are added or removed.
-  bool ClearFontCacheAndAddUserFonts();
+  bool ClearFontFaceCacheAndAddUserFonts();
 
   void ClearKeyframeRules() { keyframes_rule_map_.clear(); }
   void ClearPropertyRules();

third_party/blink/renderer/platform/fonts/font.cc

@@ -65,6 +65,20 @@ Font& Font::operator=(const Font& other) {
   return *this;
 }
 
+namespace {
+
+bool FontFallbackListVersionEqual(const FontFallbackList* first,
+                                  const FontFallbackList* second) {
+  if (RuntimeEnabledFeatures::CSSReducedFontLoadingInvalidationsEnabled())
+    return true;
+  return (first ? first->FontSelectorVersion() : 0) ==
+             (second ? second->FontSelectorVersion() : 0) &&
+         (first ? first->Generation() : 0) ==
+             (second ? second->Generation() : 0);
+}
+
+}  // namespace
+
 bool Font::operator==(const Font& other) const {
   FontSelector* first =
       font_fallback_list_ ? font_fallback_list_->GetFontSelector() : nullptr;
@@ -73,15 +87,8 @@ bool Font::operator==(const Font& other) const {
                              : nullptr;
 
   return first == second && font_description_ == other.font_description_ &&
-         (font_fallback_list_
-              ? font_fallback_list_->FontSelectorVersion()
-              : 0) == (other.font_fallback_list_
-                           ? other.font_fallback_list_->FontSelectorVersion()
-                           : 0) &&
-         (font_fallback_list_ ? font_fallback_list_->Generation() : 0) ==
-             (other.font_fallback_list_
-                  ? other.font_fallback_list_->Generation()
-                  : 0);
+         FontFallbackListVersionEqual(font_fallback_list_.get(),
+                                      other.font_fallback_list_.get());
 }
 
 namespace {