Implement ::placeholder CSS selector.

third_party/WebKit/Source/core/css/CSSSelector.cpp

 /*
  * Copyright (C) 1999-2003 Lars Knoll (knoll@kde.org)
  *               1999 Waldo Bastian (bastian@kde.org)
  *               2001 Andreas Schlapbach (schlpbch@iam.unibe.ch)
  *               2001-2003 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2002, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2008 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
@@ skipping 339 matching lines @@
     {"last-child", CSSSelector::PseudoLastChild},
     {"last-of-type", CSSSelector::PseudoLastOfType},
     {"left", CSSSelector::PseudoLeftPage},
     {"link", CSSSelector::PseudoLink},
     {"no-button", CSSSelector::PseudoNoButton},
     {"only-child", CSSSelector::PseudoOnlyChild},
     {"only-of-type", CSSSelector::PseudoOnlyOfType},
     {"optional", CSSSelector::PseudoOptional},
     {"out-of-range", CSSSelector::PseudoOutOfRange},
     {"past", CSSSelector::PseudoPastCue},
+    {"placeholder", CSSSelector::PseudoWebKitCustomElement},

[rune, 2016/11/18 09:53:23]

Making this a PseudoWebKitCustomElement means this pseudo element will get the
same treatment as -webkit-prefixed pseudo elements in certain parts of the code
like isPseudoClassValidAfterPseudoElement(). For the mentioned method it means
we're allowing user action pseudo classes after the element. What would the code
look like if we actually assigned a separate pseudo element enum for this?

[tkent, 2016/11/21 05:36:02]

Firefox and Safari don't accept user-action pseudo classes after ::placeholder. 
So this approach wasn't good.

Patch Set 2 introduces new separated enum.  Would you take another look at it
please?
I also added tests.

     {"placeholder-shown", CSSSelector::PseudoPlaceholderShown},
     {"read-only", CSSSelector::PseudoReadOnly},
     {"read-write", CSSSelector::PseudoReadWrite},
     {"required", CSSSelector::PseudoRequired},
     {"right", CSSSelector::PseudoRightPage},
     {"root", CSSSelector::PseudoRoot},
     {"scope", CSSSelector::PseudoScope},
     {"selection", CSSSelector::PseudoSelection},
     {"shadow", CSSSelector::PseudoShadow},
     {"single-button", CSSSelector::PseudoSingleButton},
@@ skipping 60 matching lines @@
   if (match == pseudoTypeMapEnd || match->string != name.getString())
     return CSSSelector::PseudoUnknown;
 
   if (match->type == CSSSelector::PseudoDefined &&
       !RuntimeEnabledFeatures::customElementsV1Enabled())
     return CSSSelector::PseudoUnknown;
 
   return static_cast<CSSSelector::PseudoType>(match->type);
 }
 
+AtomicString CSSSelector::aliasForShadowPseudoId(const AtomicString& name) {

[rune, 2016/11/18 09:53:23]

Using the term alias here could be confusing since you're not implementing it as
an alias in terms of the whatwg compat spec, but just sharing code between the
implementations.

Not sure what a better name would be.

+  if (name == "-webkit-input-placeholder")
+    return "placeholder";
+  return nullAtom;
+}
+
 #ifndef NDEBUG
 void CSSSelector::show(int indent) const {
   printf("%*sselectorText(): %s\n", indent, "", selectorText().ascii().data());
   printf("%*sm_match: %d\n", indent, "", m_match);
   if (m_match != Tag)
     printf("%*svalue(): %s\n", indent, "", value().ascii().data());
   printf("%*sgetPseudoType(): %d\n", indent, "", getPseudoType());
   if (m_match == Tag)
     printf("%*stagQName().localName: %s\n", indent, "",
            tagQName().localName().ascii().data());
@@ skipping 551 matching lines @@
     if (count < nthBValue())
       return false;
     return (count - nthBValue()) % nthAValue() == 0;
   }
   if (count > nthBValue())
     return false;
   return (nthBValue() - count) % (-nthAValue()) == 0;
 }
 
 }  // namespace blink