Implement @patch annotation for patch class members

runtime/lib/symbol_patch.dart

Index: runtime/lib/symbol_patch.dart
diff --git a/runtime/lib/symbol_patch.dart b/runtime/lib/symbol_patch.dart
index 4c70daa1e95b3bcdfd7358b1ec89a5a3ee67009e..ee52cfca6641c4ad64bd2b8bf890b10890873901 100644
--- a/runtime/lib/symbol_patch.dart
+++ b/runtime/lib/symbol_patch.dart
@@ -3,10 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 @patch class Symbol {
-  /* @patch */ const Symbol(String name)
+  @patch const Symbol(String name)
       : this._name = name;
 
-  /* @patch */ toString() => 'Symbol("${getUnmangledName(this)}")';
+  @patch toString() => 'Symbol("${getUnmangledName(this)}")';
 
   static getUnmangledName(Symbol symbol) {
     String string = Symbol.getName(symbol);
@@ -52,7 +52,7 @@
     return result.toString();
   }
 
-  /* @patch */ int get hashCode {
+  @patch int get hashCode {
     const arbitraryPrime = 664597;
     return 0x1fffffff & (arbitraryPrime * _name.hashCode);
   }