Add usage display support for Extension IME.

chrome/browser/extensions/extension_input_module_constants.cc

 // Copyright (c) 2012 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.
 
 #include "chrome/browser/extensions/extension_input_module_constants.h"
 
 namespace extension_input_module_constants {
 
 const char kAnnotationKey[] = "annotation";
 const char kAuxiliaryTextKey[] = "auxiliaryText";
@@ skipping 16 matching lines @@
 const char kParentIdKey[] = "parentId";
 const char kPropertiesKey[] = "properties";
 const char kSegmentsKey[] = "segments";
 const char kSelectionEndKey[] = "selectionEnd";
 const char kSelectionStartKey[] = "selectionStart";
 const char kStartKey[] = "start";
 const char kStyleDoubleUnderline[] = "doubleUnderline";
 const char kStyleKey[] = "style";
 const char kStyleUnderline[] = "underline";
 const char kTextKey[] = "text";
+const char kUsageBodyKey[] = "body";
+const char kUsageKey[] = "usage";
+const char kUsageTitleKey[] = "title";
 const char kVerticalKey[] = "vertical";
 const char kVisibleKey[] = "visible";
 
 }  // namespace extension_input_module_constants