Pseudo elements may only appear in rightmost compound.

third_party/WebKit/Source/core/css/parser/CSSSelectorParserTest.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/parser/CSSSelectorParser.h"
 
 #include "core/css/CSSSelectorList.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ skipping 185 matching lines @@
         CSSTokenizer::Scope scope(testCase);
         CSSParserTokenRange range = scope.tokenRange();
         CSSSelectorList list = CSSSelectorParser::parseSelector(range, CSSParserContext(HTMLStandardMode, nullptr), nullptr);
         EXPECT_FALSE(list.isValid());
     }
 }
 
 TEST(CSSSelectorParserTest, WorkaroundForInvalidCustomPseudoInUAStyle)
 {
     // See crbug.com/578131
-    CSSTokenizer::Scope scope("video::-webkit-media-text-track-region-container.scrolling");
-    CSSParserTokenRange range = scope.tokenRange();
-    CSSSelectorList list = CSSSelectorParser::parseSelector(range, CSSParserContext(UASheetMode, nullptr), nullptr);
-    EXPECT_TRUE(list.isValid());
+    const char* testCases[] = {
+        "video::-webkit-media-text-track-region-container.scrolling",
+        "input[type=\"range\" i]::-webkit-media-slider-container > div"
+    };
+
+    for (auto testCase : testCases) {
+        CSSTokenizer::Scope scope(testCase);
+        CSSParserTokenRange range = scope.tokenRange();
+        CSSSelectorList list = CSSSelectorParser::parseSelector(range, CSSParserContext(UASheetMode, nullptr), nullptr);
+        EXPECT_TRUE(list.isValid());
+    }
+}
+
+TEST(CSSSelectorParserTest, ValidPseudoElementInNonRightmostCompound)
+{
+    const char* testCases[] = {
+        "::content *",
+        "::shadow *",
+        "::content div::before",
+        "::shadow ::first-letter"
+    };
+
+    for (auto testCase : testCases) {
+        CSSTokenizer::Scope scope(testCase);
+        CSSParserTokenRange range = scope.tokenRange();
+        CSSSelectorList list = CSSSelectorParser::parseSelector(range, CSSParserContext(HTMLStandardMode, nullptr), nullptr);
+        EXPECT_TRUE(list.isValid());
+    }
+}
+
+TEST(CSSSelectorParserTest, InvalidPseudoElementInNonRightmostCompound)
+{
+    const char* testCases[] = {
+        "::-webkit-volume-slider *",
+        "::before *",
+        "::-webkit-scrollbar *",
+        "::cue *",
+        "::selection *"
+    };
+
+    for (auto testCase : testCases) {
+        CSSTokenizer::Scope scope(testCase);
+        CSSParserTokenRange range = scope.tokenRange();
+        CSSSelectorList list = CSSSelectorParser::parseSelector(range, CSSParserContext(HTMLStandardMode, nullptr), nullptr);
+        EXPECT_FALSE(list.isValid());
+    }
 }
 
 } // namespace