Fix all strong mode warnings in protoc-plugin

lib/enum_generator.dart

 // Copyright (c) 2013, 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.
 
 part of protoc;
 
 class EnumAlias {
   final EnumValueDescriptorProto value;
   final EnumValueDescriptorProto canonicalValue;
   EnumAlias(this.value, this.canonicalValue);
 }
 
 class EnumGenerator extends ProtobufContainer {
   final ProtobufContainer _parent;
   final String classname;
   final String fqname;
   final EnumDescriptorProto _descriptor;
   final List<EnumValueDescriptorProto> _canonicalValues =
       <EnumValueDescriptorProto>[];
   final List<EnumAlias> _aliases = <EnumAlias>[];
 
-  EnumGenerator(
-      EnumDescriptorProto descriptor,
-      ProtobufContainer parent)
-    : _parent = parent,
-      classname = (parent == null || parent is FileGenerator) ?
-          descriptor.name : '${parent.classname}_${descriptor.name}',
-      fqname = (parent == null || parent.fqname == null) ? descriptor.name :
-          (parent.fqname == '.' ?
-              '.${descriptor.name}' : '${parent.fqname}.${descriptor.name}'),
-      _descriptor = descriptor {
+  EnumGenerator(EnumDescriptorProto descriptor, ProtobufContainer parent)
+      : _parent = parent,
+        classname = (parent == null || parent is FileGenerator)
+            ? descriptor.name
+            : '${parent.classname}_${descriptor.name}',
+        fqname = (parent == null || parent.fqname == null)
+            ? descriptor.name
+            : (parent.fqname == '.'
+                ? '.${descriptor.name}'
+                : '${parent.fqname}.${descriptor.name}'),
+        _descriptor = descriptor {
     for (EnumValueDescriptorProto value in descriptor.value) {
       EnumValueDescriptorProto canonicalValue =
           descriptor.value.firstWhere((v) => v.number == value.number);
       if (value == canonicalValue) {
         _canonicalValues.add(value);
       } else {
         _aliases.add(new EnumAlias(value, canonicalValue));
       }
     }
   }
@@ skipping 14 matching lines @@
       return name;
     }
     return "$packageImportPrefix.$name";
   }
 
   void generate(IndentingWriter out) {
     out.addBlock('class ${classname} extends ProtobufEnum {', '}\n', () {
       // -----------------------------------------------------------------
       // Define enum types.
       for (EnumValueDescriptorProto val in _canonicalValues) {
-        out.println(
-            'static const ${classname} ${val.name} = '
-                "const ${classname}._(${val.number}, '${val.name}');");
+        out.println('static const ${classname} ${val.name} = '
+            "const ${classname}._(${val.number}, '${val.name}');");
       }
       if (!_aliases.isEmpty) {
         out.println();
         for (EnumAlias alias in _aliases) {
           out.println('static const ${classname} ${alias.value.name} ='
               ' ${alias.canonicalValue.name};');
         }
       }
       out.println();
 
-      out.println(
-        'static const List<${classname}> values ='
-            ' const <${classname}> [');
+      out.println('static const List<${classname}> values ='
+          ' const <${classname}> [');
       for (EnumValueDescriptorProto val in _canonicalValues) {
         out.println('  ${val.name},');
       }
       out.println('];');
       out.println();
 
-      out.println('static final Map<int, ${classname}> _byValue ='
+      out.println('static final Map<int, dynamic> _byValue ='
           ' ProtobufEnum.initByValue(values);');
       out.println('static ${classname} valueOf(int value) =>'
-          ' _byValue[value];');
+          ' _byValue[value] as ${classname};');
       out.addBlock('static void $checkItem($classname v) {', '}', () {
         out.println('if (v is !$classname)'
-        " checkItemFailed(v, '$classname');");
+            " checkItemFailed(v, '$classname');");
       });
       out.println();
 
       out.println('const ${classname}._(int v, String n) '
           ': super(v, n);');
     });
   }
 
   /// Writes a Dart constant containing the JSON for the EnumProtoDescriptor.
   void generateConstants(IndentingWriter out) {
     var name = getJsonConstant(fileGen);
     var json = _descriptor.writeToJsonMap();
 
     out.print("const $name = ");
     writeJsonConst(out, json);
     out.println(";");
     out.println();
   }
 }