Fix warnings in dart2js.

sdk/lib/_internal/compiler/implementation/ssa/codegen.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.
 
 part of ssa;
 
 class SsaCodeGeneratorTask extends CompilerTask {
 
   final JavaScriptBackend backend;
 
@@ skipping 260 matching lines @@
   }
 
   js.Node attachLocationRange(js.Node jsNode,
                               SourceFileLocation sourcePosition,
                               SourceFileLocation endSourcePosition) {
     jsNode.sourcePosition = sourcePosition;
     jsNode.endSourcePosition = endSourcePosition;
     return jsNode;
   }
 
-  beginGraph(HGraph graph);
-  endGraph(HGraph graph);
-
   void preGenerateMethod(HGraph graph) {
     new SsaInstructionMerger(generateAtUseSite, compiler).visitGraph(graph);
     new SsaConditionMerger(
         generateAtUseSite, controlFlowOperators).visitGraph(graph);
     SsaLiveIntervalBuilder intervalBuilder = new SsaLiveIntervalBuilder(
         compiler, generateAtUseSite, controlFlowOperators);
     intervalBuilder.visitGraph(graph);
     SsaVariableAllocator allocator = new SsaVariableAllocator(
         compiler,
         intervalBuilder.liveInstructions,
@@ skipping 2299 matching lines @@
   if (leftType.canBeNull() && rightType.canBeNull()) {
     if (left.isConstantNull() || right.isConstantNull() ||
         (leftType.isPrimitive(compiler) && leftType == rightType)) {
       return '==';
     }
     return null;
   } else {
     return '===';
   }
 }