Fix generated server code to be strong mode compliant

pkg/analysis_server/tool/spec/codegen_dart_protocol.dart

Index: pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
diff --git a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
index 02855a69bd26ce9a7be7ba2b2536bbfb7ecdd065..15a5a4808623ab34650c1a06998f4904eecf4993 100644
--- a/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
+++ b/pkg/analysis_server/tool/spec/codegen_dart_protocol.dart
@@ -970,7 +970,7 @@ class CodegenProtocolVisitor extends DartCodegenVisitor with CodeGenerator {
           if (!valueCode.isIdentity) {
             result.write(', valueDecoder: ${valueCode.asClosure}');
           }
-          result.write(')');
+          result.write(') as ${dartType(type)}');
           return result.toString();
         });
       }
@@ -980,7 +980,7 @@ class CodegenProtocolVisitor extends DartCodegenVisitor with CodeGenerator {
         return new FromJsonFunction('jsonDecoder.decodeList');
       } else {
         return new FromJsonSnippet((String jsonPath, String json) =>
-            'jsonDecoder.decodeList($jsonPath, $json, ${itemCode.asClosure})');
+            'jsonDecoder.decodeList($jsonPath, $json, ${itemCode.asClosure}) as ${dartType(type)}');

[Paul Berry, 2016/03/31 18:30:44]

Would it be possible to avoid the type cast by making decodeList a generic
function, so that instead of:

  jsonDecoder.decodeList(...) as List<Foo>

we do this instead?

  jsonDecoder.decodeList/*<Foo>*/(...)

       }
     } else if (type is TypeUnion) {
       List<String> decoders = <String>[];