Turn on many more Eclipse warnings, and fix them

- Warn on empty statements, e.g. "for (;;);". These may be
   typos and are easily replaced by "for (;;) {}" which is more
   explicit.
 - Warn on field hiding. This allows cleanup of many acceptance test
   members, at the cost of a couple of renames and the occasional
   suppression (when the field is in a public nested enum that shadows
   a public constant).
 - Warn on unnecessary casts.
 - Warn on unused declared thrown exceptions. In addition to reducing
   method signature length and number of imports, this also eliminated
   some impossible catch blocks.
 - Warn on missing @Override annotations.
 - Warn on unused parameters. This is likely the most controversial,
   as a few relatively common patterns require unused parameters in a
   way that Eclipse can't ignore. However, it also resulted in cleanup
   of a lot of unnecessary injections and method parameters, so I
   think the cost was worth it.

Change-Id: I7224be8b1c798613a127c88507e8cce400679e5d

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

@@ -28,10 +28,12 @@ public class AccountSuggestOracle extends SuggestAfterTypingNCharsOracle {
   @Override
   public void _onRequestSuggestions(final Request req, final Callback callback) {
     RpcStatus.hide(new Runnable() {
+      @Override
       public void run() {
         SuggestUtil.SVC.suggestAccount(req.getQuery(), Boolean.TRUE,
             req.getLimit(),
             new GerritCallback<List<AccountInfo>>() {
+              @Override
               public void onSuccess(final List<AccountInfo> result) {
                 final ArrayList<AccountSuggestion> r =
                     new ArrayList<>(result.size());
@@ -52,10 +54,12 @@ public class AccountSuggestOracle extends SuggestAfterTypingNCharsOracle {
       info = k;
     }
 
+    @Override
     public String getDisplayString() {
       return FormatUtil.nameEmail(FormatUtil.asInfo(info));
     }
 
+    @Override
     public String getReplacementString() {
       return FormatUtil.nameEmail(FormatUtil.asInfo(info));
     }