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

runtime/vm/kernel_binary_flowgraph.h

Index: runtime/vm/kernel_binary_flowgraph.h
diff --git a/runtime/vm/kernel_binary_flowgraph.h b/runtime/vm/kernel_binary_flowgraph.h
index f3d899be177a888837cdb0c3138af5dbbd92fd0e..8f6f723e0ba2aa119bf06e21b938035eb4e5be2d 100644
--- a/runtime/vm/kernel_binary_flowgraph.h
+++ b/runtime/vm/kernel_binary_flowgraph.h
@@ -1212,6 +1212,7 @@ class ClassHelper {
     kIsAbstract,
     kNameIndex,
     kSourceUriIndex,
+    kDocumentationCommentIndex,
     kAnnotations,
     kTypeParameters,
     kSuperClass,
@@ -1263,6 +1264,9 @@ class ClassHelper {
         builder_->current_script_id_ = source_uri_index_;
         builder_->record_token_position(position_);
         if (++next_read_ == field) return;
+      case kDocumentationCommentIndex:
+        builder_->ReadStringReference();
+        if (++next_read_ == field) return;
       case kAnnotations: {
         annotation_count_ = builder_->ReadListLength();  // read list length.
         for (intptr_t i = 0; i < annotation_count_; ++i) {