CSS4: Implement :placeholder-shown pseudo class

Source/core/css/SelectorChecker.cpp

Index: Source/core/css/SelectorChecker.cpp
diff --git a/Source/core/css/SelectorChecker.cpp b/Source/core/css/SelectorChecker.cpp
index 45134f9de9d78959dbf1e6d710c414dcf91105de..fc43f7861cc9ef34e027521c054921efb4b65eac 100644
--- a/Source/core/css/SelectorChecker.cpp
+++ b/Source/core/css/SelectorChecker.cpp
@@ -766,6 +766,15 @@ bool SelectorChecker::checkPseudoClass(const SelectorCheckingContext& context, M
             return isFirstOfType(element, element.tagQName()) && isLastOfType(element, element.tagQName());
         }
         break;
+    case CSSSelector::PseudoPlaceholderShown:
+        if (isHTMLTextFormControlElement(element)) {
+            if (m_mode == ResolvingStyle) {
+                if (ComputedStyle* style = context.elementStyle ? context.elementStyle : element.mutableComputedStyle())
+                    style->setUnique();

[esprehn, 2015/08/21 10:18:10]

This should not make you unique, change SharedStyleFinder to check
isPlaceholderVisible() when comparing input elements. Please don't copy pasta
webkit patches.

[ramya.v, 2015/08/25 10:24:45]

Done.

+            }
+            return toHTMLTextFormControlElement(element).isPlaceholderVisible();
+        }
+        break;
     case CSSSelector::PseudoNthChild:
         if (ContainerNode* parent = element.parentElementOrDocumentFragment()) {
             if (m_mode == ResolvingStyle)