Move codegen registration to transformImpact method.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

 // Copyright (c) 2014, 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.
 
 library code_generator;
 
 import 'glue.dart';
 
 import '../../closure.dart' show
     ClosureClassElement;
@@ skipping 820 matching lines @@
     }
   }
 
   @override
   js.Expression visitTypeExpression(tree_ir.TypeExpression node) {
     List<js.Expression> arguments = visitExpressionList(node.arguments);
     return glue.generateTypeRepresentation(node.dartType, arguments, registry);
   }
 
   js.Node handleForeignCode(tree_ir.ForeignCode node) {
-    registry.registerStaticUse(node.dependency);
+    if (node.dependency != null) {
+      // Dependency is only used if [node] calls a Dart function. Currently only
+      // through foreign function `RAW_DART_FUNCTION_REF`.
+      registry.registerStaticUse(node.dependency);
+    }
     // TODO(sra): Should this be in CodegenRegistry?
     glue.registerNativeBehavior(node.nativeBehavior, node);
     return node.codeTemplate.instantiate(visitExpressionList(node.arguments));
   }
 
   @override
   js.Expression visitForeignExpression(tree_ir.ForeignExpression node) {
     return handleForeignCode(node);
   }
 
@@ skipping 189 matching lines @@
   void registerDefaultParameterValues(ExecutableElement element) {
     if (element is! FunctionElement) return;
     FunctionElement function = element;
     if (function.isStatic) return; // Defaults are inlined at call sites.
     function.functionSignature.forEachOptionalParameter((param) {
       ConstantValue constant = glue.getDefaultParameterValue(param);
       registry.registerCompileTimeConstant(constant);
     });
   }
 }