Remove the skip annotation from several tests that used to cause errors but don't anymore.

Update comment in `element_builder` to have simpler phrasing.

Rename the argument in `addTypeParameter` to be more consistent.

Change-Id: Ifdb1d63e5c1c4e06fddae51e0149748b14affde5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/448663
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/analyzer/lib/src/dart/element/element.dart

@@ -4710,9 +4710,9 @@ abstract class InstanceFragmentImpl extends FragmentImpl
     fragment.enclosingFragment = this;
   }
 
-  void addTypeParameter(TypeParameterFragmentImpl typeParameter) {
-    _typeParameters.add(typeParameter);
-    typeParameter.enclosingFragment = this;
+  void addTypeParameter(TypeParameterFragmentImpl fragment) {
+    _typeParameters.add(fragment);
+    fragment.enclosingFragment = this;
   }
 }
 

pkg/analyzer/lib/src/summary2/element_builder.dart

@@ -201,7 +201,7 @@ class ElementBuilder {
         fragment.typeParameters.length = lastTypeParameterFragments.length;
       }
 
-      // Synthesize missing type parameters.
+      // Add missing type parameters.
       if (lastTypeParameterFragments.length > fragment.typeParameters.length) {
         for (
           var i = fragment.typeParameters.length;