Allow RestApi calls to receive text from handlers

Wrap the result in a NativeString, and naively cast it to whatever
the callback is asking for (which is not particularly less safe than
what we do for JSON).

Change-Id: I1807ce33544964533f8d2a88c45576c18f4394ec

gerrit-gwtui/src/main/java/com/google/gerrit/client/rpc/RestApi.java

@@ -124,17 +124,10 @@ public class RestApi {
         }
 
       } else if (200 <= status && status < 300) {
-        if (!isJsonBody(res)) {
-          if (!background) {
-            RpcStatus.INSTANCE.onRpcComplete();
-          }
-          cb.onFailure(new StatusCodeException(SC_BAD_RESPONSE, "Expected "
-              + JSON_TYPE + "; received Content-Type: "
-              + res.getHeader("Content-Type")));
-          return;
-        }
-
         T data;
+        if (isTextBody(res)) {
+          data = NativeString.wrap(res.getText()).cast();
+        } else if (isJsonBody(res)) {
           try {
             // javac generics bug
             data = RestApi.<T>cast(parseJson(res));
@@ -146,6 +139,15 @@ public class RestApi {
                 "Invalid JSON: " + e.getMessage()));
             return;
           }
+        } else {
+          if (!background) {
+            RpcStatus.INSTANCE.onRpcComplete();
+          }
+          cb.onFailure(new StatusCodeException(SC_BAD_RESPONSE, "Expected "
+              + JSON_TYPE + " or " + TEXT_TYPE + "; received Content-Type: "
+              + res.getHeader("Content-Type")));
+          return;
+        }
 
         cb.onSuccess(data);
         if (!background) {