Implement hashCode on objects stored in a set or used as map keys.

dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart

Index: dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart b/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
index 23b4f7832379d3d728e67d2c41070872890bec0e..fb4a1e0e7d9103af80137d87748042f315bff737 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/scanner/token.dart
@@ -150,6 +150,8 @@ class Token implements Spannable {
       return slowToString().length;
     }
   }
+
+  int get hashCode => computeHashCode(charOffset, info, value);
 }
 
 /**
@@ -312,6 +314,8 @@ class PrecedenceInfo {
   const PrecedenceInfo(this.value, this.precedence, this.kind);
 
   toString() => 'PrecedenceInfo($value, $precedence, $kind)';
+
+  int get hashCode => computeHashCode(value, precedence, kind);
 }
 
 // TODO(ahe): The following are not tokens in Dart.