Improve double implementation.

dart/frog/leg/ssa/builder.dart

 // 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.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 1872 matching lines @@
       push(new HAdd(target, prefix, pop()));
     }
   }
 
   visitStringInterpolationPart(StringInterpolationPart node) {
     // The parts are iterated in visitStringInterpolation.
     unreachable();
   }
 
   visitEmptyStatement(EmptyStatement node) {
-    compiler.unimplemented('SsaBuilder.visitEmptyStatement',
-                           node: node);
+    // Do nothing, empty statement.
   }
 
   visitModifiers(Modifiers node) {
     compiler.unimplemented('SsaBuilder.visitModifiers', node: node);
   }
 
   visitBreakStatement(BreakStatement node) {
     compiler.unimplemented('SsaBuilder.visitBreakStatement', node: node);
   }
 
@@ skipping 192 matching lines @@
   }
 
   visitCatchBlock(CatchBlock node) {
     visit(node.block);
   }
 
   visitTypedef(Typedef node) {
     compiler.unimplemented('SsaBuilder.visitTypedef', node: node);
   }
 }