Fix FontDescription cache keys with identical FontVariationSettings

Two identical FontDescriptions with identical font-variation-settings
axis + value pairs should produce the same FontCacheKey hash. Fix an issue
in FontCacheKey computation that only performs pointer comparisons on
the FontVariationSettings.

This fixes a smaller percentage of FontCache misses during variable font
animations.

Bug: 1046257
Change-Id: I05ae3ac64b289dc7e1c41b03ab15d7e651195d9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023650Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736280}

third_party/blink/renderer/platform/fonts/font_cache_key.h

@@ -93,13 +93,19 @@ struct FontCacheKey {
   }
 
   bool operator==(const FontCacheKey& other) const {
+    bool variation_settings_equal =
+        (!variation_settings_ && !other.variation_settings_) ||
+        (variation_settings_ && other.variation_settings_ &&
+         *variation_settings_ == *other.variation_settings_);
     return creation_params_ == other.creation_params_ &&
            font_size_ == other.font_size_ && options_ == other.options_ &&
            device_scale_factor_ == other.device_scale_factor_ &&
-           variation_settings_ == other.variation_settings_ &&
+           variation_settings_equal &&
            is_unique_match_ == other.is_unique_match_;
   }
 
+  bool operator!=(const FontCacheKey& other) const { return !(*this == other); }
+
   static constexpr unsigned PrecisionMultiplier() {
     return kFontSizePrecisionMultiplier;
   }

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

@@ -63,6 +63,78 @@ TEST(FontDescriptionTest, TestHashCollision) {
   }
 }
 
+TEST(FontDescriptionTest, VariationSettingsIdentical) {
+  FontDescription a;
+  FontDescription b(a);
+
+  scoped_refptr<FontVariationSettings> settings_a =
+      FontVariationSettings::Create();
+  settings_a->Append(FontVariationAxis("test", 1));
+
+  scoped_refptr<FontVariationSettings> settings_b =
+      FontVariationSettings::Create();
+  settings_b->Append(FontVariationAxis("test", 1));
+
+  ASSERT_EQ(*settings_a, *settings_b);
+
+  a.SetVariationSettings(settings_a);
+  b.SetVariationSettings(settings_b);
+
+  ASSERT_EQ(a, b);
+
+  FontFaceCreationParams test_creation_params;
+  FontCacheKey cache_key_a = a.CacheKey(test_creation_params, false);
+  FontCacheKey cache_key_b = b.CacheKey(test_creation_params, false);
+
+  ASSERT_EQ(cache_key_a, cache_key_b);
+}
+
+TEST(FontDescriptionTest, VariationSettingsDifferent) {
+  FontDescription a;
+  FontDescription b(a);
+
+  scoped_refptr<FontVariationSettings> settings_a =
+      FontVariationSettings::Create();
+  settings_a->Append(FontVariationAxis("test", 1));
+
+  scoped_refptr<FontVariationSettings> settings_b =
+      FontVariationSettings::Create();
+  settings_b->Append(FontVariationAxis("0000", 1));
+
+  ASSERT_NE(*settings_a, *settings_b);
+
+  a.SetVariationSettings(settings_a);
+  b.SetVariationSettings(settings_b);
+
+  ASSERT_NE(a, b);
+
+  FontFaceCreationParams test_creation_params;
+
+  FontCacheKey cache_key_a = a.CacheKey(test_creation_params, false);
+  FontCacheKey cache_key_b = b.CacheKey(test_creation_params, false);
+
+  ASSERT_NE(cache_key_a, cache_key_b);
+
+  scoped_refptr<FontVariationSettings> second_settings_a =
+      FontVariationSettings::Create();
+  second_settings_a->Append(FontVariationAxis("test", 1));
+
+  scoped_refptr<FontVariationSettings> second_settings_b =
+      FontVariationSettings::Create();
+
+  ASSERT_NE(*second_settings_a, *second_settings_b);
+
+  a.SetVariationSettings(second_settings_a);
+  b.SetVariationSettings(second_settings_b);
+
+  ASSERT_NE(a, b);
+
+  FontCacheKey second_cache_key_a = a.CacheKey(test_creation_params, false);
+  FontCacheKey second_cache_key_b = b.CacheKey(test_creation_params, false);
+
+  ASSERT_NE(second_cache_key_a, second_cache_key_b);
+}
+
 TEST(FontDescriptionTest, ToString) {
   FontDescription description;
 

third_party/blink/renderer/platform/fonts/opentype/font_settings.h

@@ -48,6 +48,7 @@ class FontSettings {
   bool operator==(const FontSettings& other) const {
     return list_ == other.list_;
   }
+  bool operator!=(const FontSettings& other) const { return !(*this == other); }
   String ToString() const {
     StringBuilder builder;
     wtf_size_t num_features = size();