Implement ::placeholder CSS selector.

third_party/WebKit/Source/core/css/parser/CSSParserSelector.h

Index: third_party/WebKit/Source/core/css/parser/CSSParserSelector.h
diff --git a/third_party/WebKit/Source/core/css/parser/CSSParserSelector.h b/third_party/WebKit/Source/core/css/parser/CSSParserSelector.h
index 40c93a6dc596ee1abf1f9de98e8bb5bc3dd6158c..f7db28ca41489c4c98d8423905b6e155ca583364 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSParserSelector.h
+++ b/third_party/WebKit/Source/core/css/parser/CSSParserSelector.h
@@ -98,6 +98,7 @@ class CORE_EXPORT CSSParserSelector {
     return pseudoType() == CSSSelector::PseudoWebKitCustomElement ||
            pseudoType() == CSSSelector::PseudoBlinkInternalElement ||
            pseudoType() == CSSSelector::PseudoCue ||
+           pseudoType() == CSSSelector::PseudoPlaceholder ||
            pseudoType() == CSSSelector::PseudoShadow ||
            pseudoType() == CSSSelector::PseudoSlotted;
   }