Add documentationComment for Class to Kernel. Parse it. Resynthesize in Analyzer.

pkg/kernel/lib/binary/ast_to_binary.dart

Index: pkg/kernel/lib/binary/ast_to_binary.dart
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index bf53b151980128746b77a12be9a011dc57ae9908..f0c2efd4299e12166ae9c8bab8bb86e9838aa7eb 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -382,6 +382,7 @@ class BinaryPrinter extends Visitor {
     writeByte(flags);
     writeStringReference(node.name ?? '');
     writeUriReference(node.fileUri ?? '');
+    writeStringReference(node.documentationComment ?? '');
     writeAnnotationList(node.annotations);
     _typeParameterIndexer.enter(node.typeParameters);
     writeNodeList(node.typeParameters);
@@ -1354,6 +1355,7 @@ class StringIndexer extends RecursiveVisitor<Null> {
   }
 
   visitClass(Class node) {
+    putOptional(node.documentationComment);
     putOptional(node.name);
     node.visitChildren(this);
   }