ChangeScreen2: Fix click inside of messages

Clicking within a message body should not collapse the message.  It
should have only the default browser behavior.

This is annoyingly obvious if a change message contains a hyperlink
and you click the link.  The message collapses but the link opens in a
new tab.  If the message had another link you also wish to follow, it
is necessary to first re-expand the message.

Move the click listener onto a new <div> that contains only the first
line (aka the header line), which is the natural click target.

Change-Id: Ic3398447df033aa69369c785166ba841f168a83d
(cherry picked from commit cd2fc945ae)

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Message.java

@@ -41,6 +41,7 @@ class Message extends Composite {
   }
 
   @UiField Style style;
+  @UiField HTMLPanel header;
   @UiField Element name;
   @UiField Element summary;
   @UiField Element date;
@@ -58,7 +59,7 @@ class Message extends Composite {
     }
 
     initWidget(uiBinder.createAndBindUi(this));
-    addDomHandler(new ClickHandler() {
+    header.addDomHandler(new ClickHandler() {
       @Override
       public void onClick(ClickEvent event) {
         setOpen(!isOpen());

gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Message.ui.xml

@@ -85,9 +85,11 @@ limitations under the License.
       addStyleNames='{style.closed}'>
     <c:AvatarImage ui:field='avatar' styleName='{style.avatar}'/>
     <div class='{style.contents}'>
+      <g:HTMLPanel ui:field='header'>
         <div class='{style.name}' ui:field='name'/>
         <div ui:field='summary' class='{style.summary}'/>
         <div class='{style.date}' ui:field='date'/>
+      </g:HTMLPanel>
       <div ui:field='message'
            aria-hidden='true'
            style='display: NONE'/>