Use closure tracer to identify closures that are not passed to Function.apply

sdk/lib/_internal/compiler/implementation/closure.dart

Index: sdk/lib/_internal/compiler/implementation/closure.dart
diff --git a/sdk/lib/_internal/compiler/implementation/closure.dart b/sdk/lib/_internal/compiler/implementation/closure.dart
index 7b1f02d7ec3417e3bcb7904fc9c57577d0a84177..b94c1c00474a5f3cb13485386a7d6e2d5267db8b 100644
--- a/sdk/lib/_internal/compiler/implementation/closure.dart
+++ b/sdk/lib/_internal/compiler/implementation/closure.dart
@@ -10,7 +10,8 @@ import "dart_types.dart";
 import "scanner/scannerlib.dart" show Token;
 import "tree/tree.dart";
 import "util/util.dart";
-import "elements/modelx.dart" show ElementX, FunctionElementX, ClassElementX;
+import "elements/modelx.dart" show ElementX, SynthesizedCallMethodElementX,
+    ClassElementX;
 import "elements/visitor.dart" show ElementVisitor;
 
 class ClosureNamer {
@@ -147,7 +148,7 @@ class ClosureClassElement extends ClassElementX {
   Node parseNode(DiagnosticListener listener) => node;
 
   /**
-   * The most outer method this closure is declared into.
+   * The element for the declaration of the function expression.
    */
   final TypedElement methodElement;
 
@@ -716,9 +717,9 @@ class ClosureTranslator extends Visitor {
     ClassElement globalizedElement = new ClosureClassElement(
         node, closureName, compiler, element, element.getCompilationUnit());
     FunctionElement callElement =
-        new FunctionElementX.from(Compiler.CALL_OPERATOR_NAME,
-                                  element,
-                                  globalizedElement);
+        new SynthesizedCallMethodElementX(Compiler.CALL_OPERATOR_NAME,
+                                          element,
+                                          globalizedElement);
     ClosureContainer enclosing = element.enclosingElement;
     enclosing.nestedClosures.add(callElement);
     globalizedElement.addMember(callElement, compiler);