Highlight comment range

Change-Id: If6744a210b4fd40a159b201543d79794970ccfd3
diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
index 7c32bf7..3fb1a50 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.ts
@@ -179,6 +179,10 @@
   @property({type: Array})
   _commentRanges: CommentRangeLayer[] = [];
 
+  // explicitly highlight a range if it is not associated with any comment
+  @property({type: Object})
+  highlightRange?: CommentRange;
+
   @property({type: Array})
   coverageRanges: CoverageRange[] = [];
 
@@ -419,6 +423,14 @@
     if (addedCommentRanges && addedCommentRanges.length) {
       this.push('_commentRanges', ...addedCommentRanges);
     }
+    if (this.highlightRange) {
+      this.push('_commentRanges', {
+        side: Side.RIGHT,
+        range: this.highlightRange,
+        hovering: true,
+        rootId: '',
+      });
+    }
   }
 
   /**
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
index 1af2adf..ec7be4a 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
@@ -317,6 +317,10 @@
     return GerritNav.getUrlForComment(changeNum, projectName, id);
   }
 
+  getHighlightRange() {
+    return this.comments?.[0]?.range;
+  }
+
   _getDiffUrlForComment(
     projectName?: RepoName,
     changeNum?: NumericChangeId,
diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
index 7d5ba11..dfb0d45 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread_html.ts
@@ -191,6 +191,7 @@
         path="[[path]]"
         prefs="[[_prefs]]"
         render-prefs="[[_renderPrefs]]"
+        highlight-range="[[getHighlightRange(comments)]]"
       >
       </gr-diff>
     </template>