blink: adds feature flag for overflow-clip

And wires up parsing of overflow:clip. This also
makes it so that if clip is set along one axis, it's
set along the other (similar to visible).

BUG=1087667
TEST=none

Change-Id: I3377d2122cf9ec2d5f938c9c67d92778a4337915
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380314Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803258}

third_party/blink/renderer/core/css/css_properties.json5

@@ -2852,7 +2852,7 @@
       property_methods: ["CSSValueFromComputedStyleInternal"],
       field_template: "keyword",
       keywords: [
-        "visible", "hidden", "scroll", "auto", "overlay"
+        "visible", "hidden", "scroll", "auto", "overlay", "clip"
       ],
       typedom_types: ["Keyword"],
       default_value: "visible",
@@ -2863,7 +2863,7 @@
       property_methods: ["CSSValueFromComputedStyleInternal"],
       field_template: "keyword",
       keywords: [
-        "visible", "hidden", "scroll", "auto", "overlay",
+        "visible", "hidden", "scroll", "auto", "overlay", "clip"
       ],
       typedom_types: ["Keyword"],
       default_value: "visible",

third_party/blink/renderer/core/css/cssom/style_property_map.cc

@@ -130,6 +130,18 @@ const CSSValue* StyleValueToCSSValue(
       }
       break;
     }
+    case CSSPropertyID::kOverflowX:
+    case CSSPropertyID::kOverflowY: {
+      if (!RuntimeEnabledFeatures::OverflowClipEnabled()) {
+        auto* identifier_value =
+            DynamicTo<CSSIdentifierValue>(style_value.ToCSSValue());
+        if (identifier_value &&
+            identifier_value->GetValueID() == CSSValueID::kClip) {
+          return nullptr;
+        }
+      }
+      break;
+    }
     case CSSPropertyID::kPaintOrder: {
       // level 1 only accepts single keywords
       const auto* value = style_value.ToCSSValue();

third_party/blink/renderer/core/css/cssom/style_property_map_test.cc

@@ -97,4 +97,51 @@ TEST_F(StylePropertyMapTest, SetRevertWithFeatureDisabled) {
   EXPECT_FALSE(y);
 }
 
+TEST_F(StylePropertyMapTest, SetOverflowClipString) {
+  ScopedOverflowClipForTest overflow_clip_feature_enabler(true);
+
+  DummyExceptionStateForTesting exception_state;
+
+  HeapVector<CSSStyleValueOrString> clip_string;
+  clip_string.push_back(CSSStyleValueOrString::FromString(" clip"));
+
+  auto* map =
+      MakeGarbageCollected<InlineStylePropertyMap>(GetDocument().body());
+
+  map->set(GetDocument().GetExecutionContext(), "overflow-x", clip_string,
+           exception_state);
+
+  CSSStyleValue* overflow = map->get(GetDocument().GetExecutionContext(),
+                                     "overflow-x", exception_state);
+  ASSERT_TRUE(DynamicTo<CSSKeywordValue>(overflow));
+  EXPECT_EQ(CSSValueID::kClip,
+            DynamicTo<CSSKeywordValue>(overflow)->KeywordValueID());
+
+  EXPECT_FALSE(exception_state.HadException());
+}
+
+TEST_F(StylePropertyMapTest, SetOverflowClipStyleValue) {
+  ScopedOverflowClipForTest overflow_clip_feature_enabler(true);
+
+  DummyExceptionStateForTesting exception_state;
+
+  HeapVector<CSSStyleValueOrString> clip_style_value;
+  clip_style_value.push_back(CSSStyleValueOrString::FromCSSStyleValue(
+      CSSKeywordValue::Create("clip", exception_state)));
+
+  auto* map =
+      MakeGarbageCollected<InlineStylePropertyMap>(GetDocument().body());
+
+  map->set(GetDocument().GetExecutionContext(), "overflow-x", clip_style_value,
+           exception_state);
+
+  CSSStyleValue* overflow = map->get(GetDocument().GetExecutionContext(),
+                                     "overflow-x", exception_state);
+  ASSERT_TRUE(DynamicTo<CSSKeywordValue>(overflow));
+  EXPECT_EQ(CSSValueID::kClip,
+            DynamicTo<CSSKeywordValue>(overflow)->KeywordValueID());
+
+  EXPECT_FALSE(exception_state.HadException());
+}
+
 }  // namespace blink

third_party/blink/renderer/core/css/parser/css_parser_fast_paths.cc

@@ -673,7 +673,9 @@ bool CSSParserFastPaths::IsValidKeywordPropertyAndValue(
       return value_id == CSSValueID::kVisible ||
              value_id == CSSValueID::kHidden ||
              value_id == CSSValueID::kScroll || value_id == CSSValueID::kAuto ||
-             value_id == CSSValueID::kOverlay;
+             value_id == CSSValueID::kOverlay ||
+             (RuntimeEnabledFeatures::OverflowClipEnabled() &&
+              value_id == CSSValueID::kClip);
     case CSSPropertyID::kBreakAfter:
     case CSSPropertyID::kBreakBefore:
       return value_id == CSSValueID::kAuto || value_id == CSSValueID::kAvoid ||

third_party/blink/renderer/core/css/parser/css_parser_fast_paths_test.cc

@@ -225,4 +225,14 @@ TEST(CSSParserFastPathsTest, ParseColorWithDecimal) {
   EXPECT_EQ(Color::kWhite, To<cssvalue::CSSColorValue>(*value).Value());
 }
 
+TEST(CSSParserFastPathsTest, IsValidKeywordPropertyAndValueOverflowClip) {
+  EXPECT_FALSE(CSSParserFastPaths::IsValidKeywordPropertyAndValue(
+      CSSPropertyID::kOverflowX, CSSValueID::kClip,
+      CSSParserMode::kHTMLStandardMode));
+  ScopedOverflowClipForTest overflow_clip_feature_enabler(true);
+  EXPECT_TRUE(CSSParserFastPaths::IsValidKeywordPropertyAndValue(
+      CSSPropertyID::kOverflowX, CSSValueID::kClip,
+      CSSParserMode::kHTMLStandardMode));
+}
+
 }  // namespace blink

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1375,6 +1375,9 @@
     {
       name: "OutOfBlinkCors",
     },
+    {
+      name: "OverflowClip",
+    },
     {
       name: "OverflowIconsForMediaControls",
     },