Add support for serializing 'target[index]' expressions.

pkg/analyzer/lib/src/summary/summarize_const_expr.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library serialization.summarize_const_expr;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
@@ skipping 223 matching lines @@
       _serialize(expr.condition);
       _serialize(expr.thenExpression);
       _serialize(expr.elseExpression);
       operations.add(UnlinkedConstOperation.conditional);
     } else if (expr is PrefixExpression) {
       _serializePrefixExpression(expr);
     } else if (expr is PropertyAccess) {
       _serializePropertyAccess(expr);
     } else if (expr is ParenthesizedExpression) {
       _serialize(expr.expression);
+    } else if (expr is IndexExpression) {
+      _serialize(expr.target);
+      _serialize(expr.index);
+      operations.add(UnlinkedConstOperation.extractIndex);
     } else {
       throw new StateError('Unknown expression type: $expr');
     }
   }
 
   void _serializeBinaryExpression(BinaryExpression expr) {
     _serialize(expr.leftOperand);
     _serialize(expr.rightOperand);
     TokenType operator = expr.operator.type;
     if (operator == TokenType.EQ_EQ) {
@@ skipping 134 matching lines @@
         expr = (expr as PrefixedIdentifier).prefix;
       } else if (expr is PropertyAccess) {
         expr = (expr as PropertyAccess).target;
       } else {
         return false;
       }
     }
     return false;
   }
 }