Fix memory leak in incremental resolver

pkg/analyzer/lib/src/context/cache.dart

Index: pkg/analyzer/lib/src/context/cache.dart
diff --git a/pkg/analyzer/lib/src/context/cache.dart b/pkg/analyzer/lib/src/context/cache.dart
index afe021626062dab159e58d4ebd91a185f7e631e1..636d2ad5f89d3e984b02f6085f2bd38dd1fbe77c 100644
--- a/pkg/analyzer/lib/src/context/cache.dart
+++ b/pkg/analyzer/lib/src/context/cache.dart
@@ -14,6 +14,8 @@ import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/task/model.dart';
 import 'package:analyzer/task/model.dart';
 
+import 'package:analyzer/src/dart/element/element.dart' show ElementImpl;
+
 /**
  * Return `true` if the given [target] is a priority one.
  */
@@ -384,7 +386,7 @@ class CacheEntry {
    * Return the value of the result represented by the given [descriptor], or
    * the default value for the result if this entry does not have a valid value.
    */
-  dynamic /*=V*/ getValue /*<V>*/ (ResultDescriptor /*<V>*/ descriptor) {
+  dynamic/*=V*/ getValue/*<V>*/(ResultDescriptor/*<V>*/ descriptor) {
     ResultData data = _resultMap[descriptor];
     if (data == null) {
       return descriptor.defaultValue;
@@ -482,8 +484,8 @@ class CacheEntry {
    * Set the value of the result represented by the given [descriptor] to the
    * given [value].
    */
-  void setValue /*<V>*/ (ResultDescriptor /*<V>*/ descriptor,
-      dynamic /*=V*/ value, List<TargetedResult> dependedOn) {
+  void setValue/*<V>*/(ResultDescriptor/*<V>*/ descriptor, dynamic/*=V*/ value,
+      List<TargetedResult> dependedOn) {
 //    {
 //      String valueStr = '$value';
 //      if (valueStr.length > 20) {
@@ -582,6 +584,10 @@ class CacheEntry {
     // If empty and not explicitly added, remove the entry altogether.
     if (_resultMap.isEmpty && !explicitlyAdded) {
       _partition.entryMap.remove(target);
+      if (target is ElementImpl) {
+        // Allow mutations now that it's no longer a map key.
+        (target as ElementImpl).frozen = false;
+      }
       _partition._removeIfSource(target);
     }
     // Notify controller.
@@ -922,6 +928,10 @@ abstract class CachePartition {
     }
     entry._partition = this;
     entry.fixExceptionState();
+    if (target is ElementImpl) {
+      // Detect attempts to mutate the map key.
+      target.frozen = true;
+    }
     entryMap[target] = entry;
     _addIfSource(target);
   }