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

pkg/front_end/lib/src/fasta/source/outline_builder.dart

Index: pkg/front_end/lib/src/fasta/source/outline_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index ca62f0ebec0f25009056b5433bf9af361220789d..c90b48bf96d77e8ae480907fcaffae3e5fc56292 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -283,6 +283,13 @@ class OutlineBuilder extends UnhandledListener {
       Token implementsKeyword,
       Token endToken) {
     debugEvent("endClassDeclaration");
+
+    String documentationComment = null;
+    if (beginToken.precedingComments != null) {
+      documentationComment = beginToken.precedingComments.lexeme;
+      // TODO(scheglov): Add support for line comments.
+    }
+
     List<TypeBuilder> interfaces = popList(interfacesCount);
     TypeBuilder supertype = pop();
     List<TypeVariableBuilder> typeVariables = pop();
@@ -294,8 +301,8 @@ class OutlineBuilder extends UnhandledListener {
     }
     int modifiers = Modifier.validate(pop());
     List<MetadataBuilder> metadata = pop();
-    library.addClass(metadata, modifiers, name, typeVariables, supertype,
-        interfaces, charOffset);
+    library.addClass(documentationComment, metadata, modifiers, name,
+        typeVariables, supertype, interfaces, charOffset);
     checkEmpty(beginToken.charOffset);
   }