Rebase on latest package:collection

test/codegen/expect/collection/src/canonicalized_map.js

 dart_library.library('collection/src/canonicalized_map', null, /* Imports */[
   'dart/_runtime',
   'dart/core',
   'collection/src/utils',
   'dart/collection'
 ], /* Lazy imports */[
 ], function(exports, dart, core, utils, collection) {
   'use strict';
   let dartx = dart.dartx;
   const _base = Symbol('_base');
@@ skipping 14 matching lines @@
         this[_canonicalize] = canonicalize;
         this[_isValidKeyFn] = isValidKey;
         this.addAll(other);
       }
       get(key) {
         if (!dart.notNull(this[_isValidKey](key))) return null;
         let pair = this[_base].get(dart.dcall(this[_canonicalize], key));
         return pair == null ? null : pair.last;
       }
       set(key, value) {
-        dart.as(key, K);
-        dart.as(value, V);
-        this[_base].set(dart.as(dart.dcall(this[_canonicalize], key), C), new (utils.Pair$(K, V))(key, value));
+        (() => {
+          dart.as(key, K);
+          dart.as(value, V);
+          if (!dart.notNull(this[_isValidKey](key))) return;
+          this[_base].set(dart.as(dart.dcall(this[_canonicalize], key), C), new (utils.Pair$(K, V))(key, value));
+        })();
         return value;
       }
       addAll(other) {
         dart.as(other, core.Map$(K, V));
         other.forEach(dart.fn((key, value) => this.set(key, value), V, [K, V]));
       }
       clear() {
         this[_base].clear();
       }
       containsKey(key) {
@@ skipping 59 matching lines @@
         [_isValidKey]: [core.bool, [core.Object]]
       })
     });
     return CanonicalizedMap;
   });
   let CanonicalizedMap = CanonicalizedMap$();
   // Exports:
   exports.CanonicalizedMap$ = CanonicalizedMap$;
   exports.CanonicalizedMap = CanonicalizedMap;
 });