v8binding: Fix CSSStyleDeclaration not to throw when a prop is deleted

Blink is implementing CSSStyleDeclaration's IDL attributes as
named properties (pretending to be IDL attributes).

Recently, the named property's implementation is improved[1] to
better conform to Web IDL specification, and "deletion of named
properties" now throws an exception when named deleter is not
defined.  So, accordingly CSSStyleDeclaration has to _better
pretend_ to have IDL attributes, which are deletable, by
defining a noop deleter.

This patch introduces such a noop deleter.

[1] https://crrev.com/c/2335713

Bug: 1121628
Change-Id: I338c064b9a2ea88fa97169a9e904da0a8613e0ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2377035Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801768}

third_party/blink/renderer/core/css/css_style_declaration.cc

@@ -196,6 +196,13 @@ NamedPropertySetterResult CSSStyleDeclaration::AnonymousNamedSetter(
   return NamedPropertySetterResult::kIntercepted;
 }
 
+NamedPropertyDeleterResult CSSStyleDeclaration::AnonymousNamedDeleter(
+    const AtomicString& name) {
+  // Pretend to be deleted since web author can define their own property with
+  // the same name.
+  return NamedPropertyDeleterResult::kDeleted;
+}
+
 void CSSStyleDeclaration::NamedPropertyEnumerator(Vector<String>& names,
                                                   ExceptionState&) {
   typedef Vector<String, numCSSProperties - 1> PreAllocatedPropertyVector;

third_party/blink/renderer/core/css/css_style_declaration.h

@@ -102,6 +102,7 @@ class CORE_EXPORT CSSStyleDeclaration : public ScriptWrappable,
   NamedPropertySetterResult AnonymousNamedSetter(ScriptState*,
                                                  const AtomicString& name,
                                                  const String& value);
+  NamedPropertyDeleterResult AnonymousNamedDeleter(const AtomicString& name);
   void NamedPropertyEnumerator(Vector<String>& names, ExceptionState&);
   bool NamedPropertyQuery(const AtomicString&, ExceptionState&);
 

third_party/blink/renderer/core/css/css_style_declaration.idl

@@ -40,4 +40,5 @@
     // https://drafts.csswg.org/cssom/#dom-cssstyledeclaration-dashed-attribute
     [Affects=Nothing] getter DOMString (DOMString name);
     [CEReactions, CallWith=ScriptState] setter void (DOMString property, [TreatNullAs=EmptyString] DOMString propertyValue);
+    deleter void (DOMString property);
 };