Update Symbol.hashCode

tool/input_sdk/patch/internal_patch.dart

Index: tool/input_sdk/patch/internal_patch.dart
diff --git a/tool/input_sdk/patch/internal_patch.dart b/tool/input_sdk/patch/internal_patch.dart
index 3684b5b3bdc0233fe39bb27958bcaa1a06efbe14..e4fd296c2c66dba6f771385167e5e068fae72397 100644
--- a/tool/input_sdk/patch/internal_patch.dart
+++ b/tool/input_sdk/patch/internal_patch.dart
@@ -5,12 +5,23 @@
 import 'dart:_js_primitives' show printString;
 import 'dart:_js_helper' show patch;
 import 'dart:_interceptors' show JSArray;
+import 'dart:_foreign_helper' show JS;
 
 @patch
 class Symbol implements core.Symbol {
   @patch
   const Symbol(String name)
       : this._name = name;
+
+  @patch
+  int get hashCode {
+    int hash = JS('int|Null', '#._hashCode', this);
+    if (hash != null) return hash;
+    const arbitraryPrime = 664597;
+    hash = 0x1fffffff & (arbitraryPrime * _name.hashCode);
+    JS('', '#._hashCode = #', this, hash);
+    return hash;
+  }
 }
 
 @patch