Omnibox.mojom: make input_string non-nullable.

chrome/browser/ui/webui/omnibox/omnibox.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The structures here roughly mirror those from autocomplete.
 
 struct AutocompleteAdditionalInfo {
   string key;
   string value;
 };
@@ skipping 31 matching lines @@
   // Time delta since the request was started, in milliseconds.
   int32 time_since_omnibox_started_ms;
   string host;
   bool is_typed_host;
   AutocompleteMatchMojo[] combined_results;
   AutocompleteResultsForProviderMojo[] results_by_provider;
 };
 
 [Client=OmniboxPage]
 interface OmniboxUIHandlerMojo {
-  // TODO(yzshen): Conceptually |input_string| could be non-nullable. However,
-  // crbug.com/407258 (JavaScript encoder encodes empty string as null) prevents
-  // us from doing so. Change it into non-nullable once the bug is resolved.
-  StartOmniboxQuery(string? input_string,
+  StartOmniboxQuery(string input_string,
                     int32 cursor_position,
                     bool prevent_inline_autocomplete,
                     bool prefer_keyword,
                     int32 page_classification);
 };
 
 interface OmniboxPage {
   HandleNewAutocompleteResult(OmniboxResultMojo result);
 };