Update dart:mirrors to use Symbol.

dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart

Index: dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart b/dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
index 6569d60ea5489c18b0ad41332af11e55d5f355b6..ec457089287b4236edf12d9ffc42077d0ddfd01a 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/lib/core_patch.dart
@@ -298,19 +298,3 @@ patch class StackTrace {
     throw new UnsupportedError('stackTrace');
   }
 }
-
-patch class Symbol {
-  final String _name;
-
-  patch const Symbol(String name) :
-    this._name = name;
-
-  patch bool operator ==(other) {
-    return other is Symbol && _name == other._name;
-  }
-
-  patch int get hashCode {
-    const arbitraryPrime = 664597;
-    return 0x1fffffff & (arbitraryPrime * _name.hashCode);
-  }
-}