Code changes to avoid Firefox debug 'error' lint warnings.

pkg/compiler/lib/src/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.
 
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/tasks.dart' show CompilerTask;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 1478 matching lines @@
     use(node.inputs[0]);
     js.Expression test = pop();
 
     HStatementInformation thenGraph = info.thenGraph;
     HStatementInformation elseGraph = info.elseGraph;
     js.Statement thenPart =
         unwrapStatement(generateStatementsInNewBlock(thenGraph));
     js.Statement elsePart =
         unwrapStatement(generateStatementsInNewBlock(elseGraph));
 
-    pushStatement(new js.If(test, thenPart, elsePart)
-        .withSourceInformation(node.sourceInformation));
+    js.Statement code;
+    // Peephole rewrites:
+    //
+    //     if (e); else S;   -->   if(!e) S;
+    //
+    //     if (e);   -->   e;
+    //
+    // TODO(sra): This peephole optimization would be better done as an SSA
+    // optimization.
+    if (thenPart is js.EmptyStatement) {
+      if (elsePart is js.EmptyStatement) {
+        code = new js.ExpressionStatement(test);
+      } else {
+        code = new js.If.noElse(new js.Prefix('!', test), elsePart);
+      }
+    } else {
+      code = new js.If(test, thenPart, elsePart);
+    }
+    pushStatement(code.withSourceInformation(node.sourceInformation));
   }
 
   visitIf(HIf node) {
     if (tryControlFlowOperation(node)) return;
 
     HInstruction condition = node.inputs[0];
     HIfBlockInformation info = node.blockInformation.body;
 
     if (condition.isConstant()) {
       HConstant constant = condition;
@@ skipping 1385 matching lines @@
     registry.registerStaticUse(new StaticUse.staticInvoke(
         helper, new CallStructure.unnamed(argumentCount)));
     return backend.emitter.staticFunctionAccess(helper);
   }
 
   @override
   void visitRef(HRef node) {
     visit(node.value);
   }
 }