Remove never-reached if block in StyleSheetContents::WrapperDeleteRule

|StyleSheetContents::import_rules_| is of type
HeapVector<Member<StyleRuleImport>>. Its members will always
resolve |import_rules_[index]->IsFontFaceRule()| to false (once
StyleRuleBase::IsImportRule() is the one that resolves to true.

This CL removes the if-block that checks that altogether,
allowing the removal of the remaining DEFINE_STYLE_RULE_TYPE_CASTS
occurrence.

Note: This was caught because trying to use To<StyleRuleFaceRule>
failed to compile.

  ../../third_party/blink/renderer/platform/wtf/casting.h:102:10: error:
  non-const lvalue reference to type 'blink::StyleRuleFontFace'
  cannot bind to a value of unrelated type 'blink::StyleRuleImport'
  return static_cast<Derived&>(from);
         ^                     ~~~~

R=jbroman@chromium.org
CC=​blink-reviews-vendor@chromium.org

BUG=891908

Change-Id: I6bbf992b3654601a50fc68b18961de79899d5284
Reviewed-on: https://chromium-review.googlesource.com/c/1496056Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#636879}

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

@@ -371,12 +371,6 @@ class CORE_EXPORT StyleRuleFontFeatureValues : public StyleRuleBase {
   Member<const CSSIdentifierValue> font_display_;
 };
 
-#define DEFINE_STYLE_RULE_TYPE_CASTS(Type)                \
-  DEFINE_TYPE_CASTS(StyleRule##Type, StyleRuleBase, rule, \
-                    rule->Is##Type##Rule(), rule.Is##Type##Rule())
-
-DEFINE_STYLE_RULE_TYPE_CASTS(FontFace);
-
 template <>
 struct DowncastTraits<StyleRule> {
   static bool AllowFrom(const StyleRuleBase& rule) {

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

@@ -284,11 +284,6 @@ bool StyleSheetContents::WrapperDeleteRule(unsigned index) {
 
   if (index < import_rules_.size()) {
     import_rules_[index]->ClearParentStyleSheet();
-    // TODO(tonikitoo): If |import_rules_| members are of type
-    // blink::StyleRuleImport, the if-check blink::StyleRuleBase::IsFontFaceRule
-    // is never going to resolve to true. Get rid of it altogether?
-    if (import_rules_[index]->IsFontFaceRule())
-      NotifyRemoveFontFaceRule(ToStyleRuleFontFace(import_rules_[index].Get()));
     import_rules_.EraseAt(index);
     return true;
   }