Add the ability to summarize inferred types based on function-typed parameters.

pkg/analyzer/lib/src/dart/element/type.dart

Index: pkg/analyzer/lib/src/dart/element/type.dart
diff --git a/pkg/analyzer/lib/src/dart/element/type.dart b/pkg/analyzer/lib/src/dart/element/type.dart
index 0f8ec27422f1043550d33383de72ccce8ae0200f..b06d584de2173a51212b0d847aaaeb2807938576 100644
--- a/pkg/analyzer/lib/src/dart/element/type.dart
+++ b/pkg/analyzer/lib/src/dart/element/type.dart
@@ -18,6 +18,11 @@ import 'package:analyzer/src/generated/type_system.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 
 /**
+ * Type of callbacks used by [DeferredFunctionTypeImpl].
+ */
+typedef FunctionTypedElement FunctionTypedElementComputer();
+
+/**
  * A [Type] that represents the type 'bottom'.
  */
 class BottomTypeImpl extends TypeImpl {
@@ -90,6 +95,41 @@ class CircularTypeImpl extends DynamicTypeImpl {
 }
 
 /**
+ * The type of a function, method, constructor, getter, or setter that has been
+ * resynthesized from a summary.  The actual underlying element won't be
+ * constructed until it's needed.
+ */
+class DeferredFunctionTypeImpl extends FunctionTypeImpl {
+  /**
+   * Callback which should be invoked when the element associated with this
+   * function type is needed.
+   *
+   * Once the callback has been invoked, it is set to `null` to reduce GC
+   * pressure.
+   */
+  FunctionTypedElementComputer _computeElement;
+
+  /**
+   * If [_computeElement] has been called, the value it returned.  Otherwise
+   * `null`.
+   */
+  FunctionTypedElement _computedElement;
+
+  DeferredFunctionTypeImpl(this._computeElement, String name,
+      List<DartType> typeArguments, bool isInstantiated)
+      : super._(null, name, null, typeArguments, isInstantiated);
+
+  @override
+  FunctionTypedElement get element {
+    if (_computeElement != null) {
+      _computedElement = _computeElement();
+      _computeElement = null;
+    }
+    return _computedElement;
+  }
+}
+
+/**
  * The [Type] representing the type `dynamic`.
  */
 class DynamicTypeImpl extends TypeImpl {
@@ -1941,7 +1981,8 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
    * If there is a single type which is at least as specific as all of the
    * types in [types], return it.  Otherwise return `null`.
    */
-  static DartType _findMostSpecificType(List<DartType> types, TypeSystem typeSystem) {
+  static DartType _findMostSpecificType(
+      List<DartType> types, TypeSystem typeSystem) {
     // The << relation ("more specific than") is a partial ordering on types,
     // so to find the most specific type of a set, we keep a bucket of the most
     // specific types seen so far such that no type in the bucket is more