Fix for text selection in comment

The change https://gerrit-review.googlesource.com/c/gerrit/+/289250
broke text selection in comment in diff-view.

Change-Id: I59c78bbb2958f7543780d4712832bff8a14724e5
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
index eebcb15..038153a 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff-utils.ts
@@ -83,7 +83,7 @@
 // For Gerrit these are instances of GrCommentThread, but other gr-diff users
 // have different HTML elements in use for comment threads.
 // TODO: Also document the required HTML attritbutes that thread elements must
-// have, e.g. 'comment-side', 'range', 'line-num', 'data-value'.
+// have, e.g. 'diff-side', 'range', 'line-num', 'data-value'.
 export interface GrDiffThreadElement extends HTMLElement {
   rootId: string;
 }
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_html.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_html.ts
index 2c8b704..557d1eb 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_html.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff_html.ts
@@ -552,9 +552,9 @@
 
     /** Make comments selectable when selected */
     .selected-left.selected-comment
-      ::slotted(gr-comment-thread[comment-side='left']),
+      ::slotted(gr-comment-thread[diff-side='left']),
     .selected-right.selected-comment
-      ::slotted(gr-comment-thread[comment-side='right']) {
+      ::slotted(gr-comment-thread[diff-side='right']) {
       -webkit-user-select: text;
       -moz-user-select: text;
       -ms-user-select: text;