Fixes to mock SDK to enable dart:core to be summarized.

pkg/analyzer/test/generated/compile_time_error_code_test.dart

Index: pkg/analyzer/test/generated/compile_time_error_code_test.dart
diff --git a/pkg/analyzer/test/generated/compile_time_error_code_test.dart b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
index a30a2cb337c78253f77561896960fe20c6738d55..5f2abf5255e11f92317a1ebba3917166fee88343 100644
--- a/pkg/analyzer/test/generated/compile_time_error_code_test.dart
+++ b/pkg/analyzer/test/generated/compile_time_error_code_test.dart
@@ -1968,8 +1968,7 @@ class C = a.A with M;'''
     Source source = addSource("class A extends double {}");
     computeLibrarySourceErrors(source);
     assertErrors(source, [
-      CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS,
-      CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_IMPLICIT
+      CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS
     ]);
     verify([source]);
   }
@@ -1998,8 +1997,7 @@ class C = a.A with M;'''
     Source source = addSource("class A extends num {}");
     computeLibrarySourceErrors(source);
     assertErrors(source, [
-      CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS,
-      CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_IMPLICIT
+      CompileTimeErrorCode.EXTENDS_DISALLOWED_CLASS
     ]);
     verify([source]);
   }