Add HTML template for change comment emails

Upgrade comment emails to emit HTML bodies in addition to the existing
plain-text message bodies. The format of the HTML body is remains
similar to the plain-text format, with the following small changes:

* File links are anchor tags rather than plain URLs.
* Parent comment quotations are set in BLOCKQUOTE tags rather than
  prefixed by the > character.
* Code quotations are monospaced rather than set in a
  proportionate-width font.
* Mult-line code quotations are set in BLOCKQUOTE tags rather than
  being prefixed by spaces followed by a colon.
* File groupings are set in nested UL & and LI tags rather than
  separating groups with an extra line feed.

Change-Id: I2ac21961b6d48e3fb3455ca6a3e30d86e50b567c

gerrit-server/src/main/java/com/google/gerrit/server/mail/CommentSender.java

@@ -136,11 +136,17 @@ public class CommentSender extends ReplyToChangeSender {
   @Override
   public void formatChange() throws EmailException {
     appendText(textTemplate("Comment"));
+    if (useHtml()) {
+      appendHtml(soyHtmlTemplate("CommentHtml"));
+    }
   }
 
   @Override
   public void formatFooter() throws EmailException {
     appendText(textTemplate("CommentFooter"));
+    if (useHtml()) {
+      appendHtml(soyHtmlTemplate("CommentFooterHtml"));
+    }
   }
 
   /**
@@ -469,6 +475,7 @@ public class CommentSender extends ReplyToChangeSender {
           commentData.put("isRobotComment", true);
           commentData.put("robotId", robotComment.robotId);
           commentData.put("robotRunId", robotComment.robotRunId);
+          commentData.put("robotUrl", robotComment.url);
         } else {
           commentData.put("isRobotComment", false);
         }
@@ -521,4 +528,9 @@ public class CommentSender extends ReplyToChangeSender {
       return "";
     }
   }
+
+  @Override
+  protected boolean supportsHtml() {
+    return true;
+  }
 }

gerrit-server/src/main/java/com/google/gerrit/server/mail/MailSoyTofuProvider.java

@@ -44,7 +44,9 @@ public class MailSoyTofuProvider implements Provider<SoyTofu> {
     "ChangeFooterHtml.soy",
     "ChangeSubject.soy",
     "Comment.soy",
+    "CommentHtml.soy",
     "CommentFooter.soy",
+    "CommentFooterHtml.soy",
     "DeleteReviewer.soy",
     "DeleteReviewerHtml.soy",
     "DeleteVote.soy",