Revise ui::DomKey to unify character and non-character codes.

ui/events/keycodes/dom/keycode_converter.h

 // Copyright 2013 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.
 
 #ifndef UI_EVENTS_KEYCODES_DOM4_KEYCODE_CONVERTER_H_
 #define UI_EVENTS_KEYCODES_DOM4_KEYCODE_CONVERTER_H_
 
 #include <stdint.h>
+#include <string>
+
 #include "base/basictypes.h"
+#include "ui/events/keycodes/dom/dom_key.h"
 
 // For reference, the W3C UI Event spec is located at:
 // http://www.w3.org/TR/uievents/
 
 namespace ui {
 
 enum class DomCode;
-enum class DomKey;
 
 enum class DomKeyLocation { STANDARD, LEFT, RIGHT, NUMPAD };
 
 // This structure is used to define the keycode mapping table.
 // It is defined here because the unittests need access to it.
 typedef struct {
   // USB keycode:
   //  Upper 16-bits: USB Usage Page.
   //  Lower 16-bits: USB Usage Id: Assigned ID within this usage page.
   uint32_t usb_keycode;
@@ skipping 29 matching lines @@
   // Convert a DomCode into a UI Events |code| string value.
   static const char* DomCodeToCodeString(DomCode dom_code);
 
   // Return the DomKeyLocation of a DomCode. The DomKeyLocation distinguishes
   // keys with the same meaning, and therefore the same DomKey or non-located
   // KeyboardCode (VKEY), and corresponds to the DOM UI Events
   // |KeyboardEvent.location|.
   static DomKeyLocation DomCodeToLocation(DomCode dom_code);
 
   // Convert a UI Events |key| string value into a DomKey.
+  // Accepts a character string containing either
+  // - a key name from http://www.w3.org/TR/DOM-Level-3-Events-key/, or
+  // - a single Unicode character (represented in UTF-8).
+  // Returns DomKey::NONE for other inputs, including |nullptr|.
   static DomKey KeyStringToDomKey(const char* key);
 
   // Convert a DomKey into a UI Events |key| string value.
-  static const char* DomKeyToKeyString(DomKey dom_key);
+  // For an invalid DomKey, returns an empty string.
+  static std::string DomKeyToKeyString(DomKey dom_key);
 
   // Returns true if the DomKey is a modifier.
   static bool IsDomKeyForModifier(DomKey dom_key);
 
   // The following methods relate to USB keycodes.
   // Note that USB keycodes are not part of any web standard.
   // Please don't use USB keycodes in new code.
 
   // Return the value that identifies an invalid USB keycode.
   static uint32_t InvalidUsbKeycode();
@@ skipping 18 matching lines @@
   static const KeycodeMapEntry* GetKeycodeMapForTest();
   static const char* DomKeyStringForTest(size_t index);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(KeycodeConverter);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_KEYCODES_DOM4_KEYCODE_CONVERTER_H_