Add type inference for complex assignments whose LHS is an index expression.

pkg/analyzer/test/src/task/strong/front_end_inference_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:front_end/src/base/instrumentation.dart' as fasta;
 import 'package:front_end/src/fasta/compiler_context.dart' as fasta;
 import 'package:front_end/src/fasta/testing/validating_instrumentation.dart'
     as fasta;
@@ skipping 423 matching lines @@
         node.prefix.staticElement is! ClassElement) {
       if (node.identifier.inGetterContext() ||
           node.identifier.inSetterContext()) {
         _recordTarget(node.identifier.offset, node.identifier.staticElement);
       }
     }
   }
 
   visitPrefixExpression(PrefixExpression node) {
     super.visitPrefixExpression(node);
-    _recordTarget(node.operator.charOffset, node.staticElement);
+    if (node.operator.type != TokenType.PLUS_PLUS &&
+        node.operator.type != TokenType.MINUS_MINUS) {
+      _recordTarget(node.operator.charOffset, node.staticElement);
+    }
   }
 
   @override
   visitPropertyAccess(PropertyAccess node) {
     super.visitPropertyAccess(node);
     if (node.propertyName.inGetterContext() ||
         node.propertyName.inSetterContext()) {
       _recordTarget(node.propertyName.offset, node.propertyName.staticElement);
     }
   }
@@ skipping 81 matching lines @@
 
   /// Based on DDC code generator's `_recoverTypeArguments`
   Iterable<DartType> _recoverTypeArguments(FunctionType g, FunctionType f) {
     assert(identical(g.element, f.element));
     assert(g.typeFormals.isNotEmpty && f.typeFormals.isEmpty);
     assert(g.typeFormals.length + g.typeArguments.length ==
         f.typeArguments.length);
     return f.typeArguments.skip(g.typeArguments.length);
   }
 }