Add HasSubclasses function to class hierarchy analysis.

runtime/vm/class_table_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/assert.h"
 #include "vm/class_finalizer.h"
 #include "vm/class_table.h"
 #include "vm/dart_entry.h"
 #include "vm/globals.h"
 #include "vm/symbols.h"
@@ skipping 102 matching lines @@
   ZoneGrowableArray<Function*>* bars =
       class_table->GetNamedInstanceFunctionsOf(*a_subclass_ids,
                                                function_bar_name);
   EXPECT_EQ(1, bars->length());
   EXPECT_EQ(class_d_bar.raw(), (*bars)[0]->raw());
 
   ZoneGrowableArray<Function*>* class_a_bar_overrides =
       class_table->GetOverridesOf(class_a_bar);
   EXPECT_EQ(1, class_a_bar_overrides->length());
   EXPECT_EQ(class_d_bar.raw(), (*class_a_bar_overrides)[0]->raw());
+
+  EXPECT(class_table->HasSubclasses(class_a_id));
+  EXPECT(class_table->HasSubclasses(class_b_id));
+  EXPECT(!class_table->HasSubclasses(class_c_id));
+  EXPECT(!class_table->HasSubclasses(class_d_id));
 }
 
 }  // namespace dart