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

sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart

Index: sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart b/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart
index 2c45b4a7cfb26310f3db12553878459ff31f7d63..b6cb9391c764f1f7afbd3827076f15bcbc5ea6ea 100644
--- a/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/inferrer/type_graph_nodes.dart
@@ -28,9 +28,13 @@ abstract class TypeInformation {
   /// Initially empty.
   TypeMask type = const TypeMask.nonNullEmpty();
 
-  /// We give up on inferencing for special elements, as well as for
-  /// complicated cyclic dependencies.
+  /// We abandon inference in certain cases (complex cyclic flow, native
+  /// behaviours, etc.). In some case, we might resume inference in the
+  /// closure tracer, which is handled by checking whether [assignments] has
+  /// been set to [STOP_TRACKING_ASSIGNMENTS_MARKER].
   bool abandonInferencing = false;
+  bool get mightResume =>
+      !identical(assignments, STOP_TRACKING_ASSIGNMENTS_MARKER);
 
   /// Number of times this [TypeInformation] has changed type.
   int refineCount = 0;
@@ -66,7 +70,10 @@ abstract class TypeInformation {
     users.remove(user);
   }
 
-  static final STOP_TRACKING_ASSIGNMENTS_MARKER =  const <TypeInformation>[];
+  // The below is not a compile time constant to make it differentiable
+  // from other empty lists of [TypeInformation].
+  static final STOP_TRACKING_ASSIGNMENTS_MARKER =
+      new List<TypeInformation>.from([], growable: false);
 
   bool areAssignmentsTracked() {
     return assignments != STOP_TRACKING_ASSIGNMENTS_MARKER;
@@ -104,7 +111,7 @@ abstract class TypeInformation {
     // Do not remove [this] as a user of nodes in [assignments],
     // because our tracing analysis could be interested in tracing
     // this node.
-    if (clearAssignments) assignments = const <TypeInformation>[];
+    if (clearAssignments) assignments = STOP_TRACKING_ASSIGNMENTS_MARKER;
     // Do not remove users because our tracing analysis could be
     // interested in tracing the users of this node.
   }
@@ -131,7 +138,7 @@ abstract class TypeInformation {
   /// Returns whether the type cannot change after it has been
   /// inferred.
   bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return !abandonInferencing && assignments.every((e) => e.isStable);
+    return !mightResume && assignments.every((e) => e.isStable);
   }
 
   void removeAndClearReferences(TypeGraphInferrerEngine inferrer) {
@@ -147,6 +154,12 @@ abstract class TypeInformation {
   }
 }
 
+abstract class ApplyableTypeInformation extends TypeInformation {
+  bool mightBePassedToFunctionApply = false;
+
+  ApplyableTypeInformation([users, assignments]) : super(users, assignments);
+}
+
 /**
  * Parameters of instance functions behave differently than other
  * elements because the inferrer may remove assignments. This happens
@@ -212,7 +225,7 @@ class ParameterAssignments extends IterableBase<TypeInformation> {
  *   trust their type annotation.
  *
  */
-class ElementTypeInformation extends TypeInformation {
+class ElementTypeInformation extends ApplyableTypeInformation  {
   final Element element;
 
   // Marker to disable [handleSpecialCases]. For example, parameters
@@ -272,7 +285,9 @@ class ElementTypeInformation extends TypeInformation {
     return count == 1;
   }
 
-  bool isClosurized() => closurizedCount > 0;
+  bool get isClosurized => closurizedCount > 0;
+
+  bool get isStable => super.isStable && !isClosurized;
 
   TypeMask handleSpecialCases(TypeGraphInferrerEngine inferrer) {
     if (abandonInferencing) return type;
@@ -397,7 +412,9 @@ class ElementTypeInformation extends TypeInformation {
     }
     // If the method is closurized, the closure tracing phase will go
     // through the users.
-    if (closurizedCount != 0) return false;
+    if (isClosurized) return false;
+
+    if (element.isFunction()) return false;
 
     return super.hasStableType(inferrer);
   }
@@ -413,7 +430,7 @@ class ElementTypeInformation extends TypeInformation {
  * any assignment. They rely on the [caller] field for static calls,
  * and [selector] and [receiver] fields for dynamic calls.
  */
-abstract class CallSiteTypeInformation extends TypeInformation {
+abstract class CallSiteTypeInformation extends ApplyableTypeInformation {
   final Spannable call;
   final Element caller;
   final Selector selector;
@@ -1233,7 +1250,7 @@ class PhiElementTypeInformation extends TypeInformation {
   }
 }
 
-class ClosureTypeInformation extends TypeInformation {
+class ClosureTypeInformation extends ApplyableTypeInformation {
   final ast.Node node;
   final Element element;