Consistently define default serialVersionUID

A handful of classes suppressed the warning instead of adding a default
serialVersionUID. I only weakly believe that using a default
serialVersionUID is better than suppressing the warning in these cases,
but I do value consistency.

Change-Id: Ic56ecb2d541c5276a9d32ab822b510598be86600

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

@@ -248,8 +248,9 @@ class RelatedChangesTab implements IsWidget {
     }
   }
 
-  @SuppressWarnings("serial")
   private class RowSafeHtml implements SafeHtml {
+    private static final long serialVersionUID = 1L;
+
     private String html;
     private ChangeAndCommit info;
     private final boolean notConnected;

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/RevisionInfoCache.java

@@ -35,10 +35,11 @@ public class RevisionInfoCache {
 
   private final LinkedHashMap<PatchSet.Id, String> psToCommit;
 
-  @SuppressWarnings("serial")
   private RevisionInfoCache() {
     psToCommit =
         new LinkedHashMap<PatchSet.Id, String>(LIMIT) {
+          private static final long serialVersionUID = 1L;
+
           @Override
           protected boolean removeEldestEntry(Map.Entry<PatchSet.Id, String> e) {
             return size() > LIMIT;

gerrit-gwtui/src/main/java/com/google/gerrit/client/ui/NavigationTable.java

@@ -73,9 +73,10 @@ public abstract class NavigationTable<RowItem> extends FancyFlexTable<RowItem> {
     }
   }
 
-  @SuppressWarnings("serial")
   private static final LinkedHashMap<String, Object> savedPositions =
       new LinkedHashMap<String, Object>(10, 0.75f, true) {
+        private static final long serialVersionUID = 1L;
+
         @Override
         protected boolean removeEldestEntry(Entry<String, Object> eldest) {
           return size() >= 20;