Marked parsing as failed for invalid compound.

If we return nullptr trying to consume a compound, and all tokens have
been consumed, we don't recognize that as a parse failure if a valid
selector precedes the compound. Set m_failedParsing to true to notice
we have an invalid selector.

R=timloh@chromium.org
BUG=581257

Review URL: https://codereview.chromium.org/1634273003

Cr-Commit-Position: refs/heads/master@{#371760}

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

@@ -291,8 +291,10 @@ PassOwnPtr<CSSParserSelector> CSSSelectorParser::consumeCompoundSelector(CSSPars
         // TODO(rune@opera.com): crbug.com/578131
         // The UASheetMode check is a work-around to allow this selector in mediaControls(New).css:
         // video::-webkit-media-text-track-region-container.scrolling
-        if (m_context.mode() != UASheetMode && !isSimpleSelectorValidAfterPseudoElement(*simpleSelector.get(), compoundPseudoElement))
+        if (m_context.mode() != UASheetMode && !isSimpleSelectorValidAfterPseudoElement(*simpleSelector.get(), compoundPseudoElement)) {
+            m_failedParsing = true;
             return nullptr;
+        }
         if (simpleSelector->match() == CSSSelector::PseudoElement)
             compoundPseudoElement = simpleSelector->pseudoType();
 

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

@@ -190,7 +190,8 @@ TEST(CSSSelectorParserTest, InvalidSimpleAfterPseudoElementInCompound)
         "::shadow:not(::after)",
         "::content:not(#id)",
         "::-webkit-scrollbar:vertical:not(:first-child)",
-        "video::-webkit-media-text-track-region-container.scrolling"
+        "video::-webkit-media-text-track-region-container.scrolling",
+        "div ::before.a"
     };
 
     for (auto testCase : testCases) {