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

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

Index: sdk/lib/_internal/compiler/implementation/elements/modelx.dart
diff --git a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
index 87828ea0989020930d9fa18c86a63e945ffb918d..d3368ca6630e5304ba5081828156d12a9c52cb03 100644
--- a/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
+++ b/sdk/lib/_internal/compiler/implementation/elements/modelx.dart
@@ -1523,14 +1523,6 @@ class FunctionElementX extends ElementX with AnalyzableElement
       : this.tooMuchOverloading(name, node, kind, modifiers, enclosing, null,
                                 false);
 
-  FunctionElementX.from(String name,
-                        FunctionElement other,
-                        Element enclosing)
-      : this.tooMuchOverloading(name, other.node, other.kind,
-                                other.modifiers, enclosing,
-                                other.functionSignature,
-                                false);
-
   FunctionElementX.tooMuchOverloading(String name,
                                       FunctionExpression this.cachedNode,
                                       ElementKind kind,
@@ -1664,6 +1656,19 @@ class FunctionElementX extends ElementX with AnalyzableElement
   accept(ElementVisitor visitor) => visitor.visitFunctionElement(this);
 }
 
+class SynthesizedCallMethodElementX extends FunctionElementX {
+  final FunctionElement expression;
+
+  SynthesizedCallMethodElementX(String name,
+                                FunctionElement other,
+                                Element enclosing)
+      : expression = other,
+        super.tooMuchOverloading(name, other.node, other.kind,
+                                 other.modifiers, enclosing,
+                                 other.functionSignature,
+                                 false);
+}
+
 class DeferredLoaderGetterElementX extends FunctionElementX {
 
   final PrefixElement prefix;