Build key map DomCodeToKey() for Windows

ui/events/keycodes/platform_key_map_win.h

+// Copyright (c) 2016 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_PLATFORM_KEY_MAP_WIN_H_
+#define UI_EVENTS_KEYCODES_PLATFORM_KEY_MAP_WIN_H_
+
+#include <windows.h>
+
+#include <unordered_map>
+
+#include "base/hash.h"
+#include "ui/events/events_base_export.h"
+#include "ui/events/keycodes/dom/dom_key.h"
+#include "ui/events/keycodes/keyboard_codes_win.h"
+
+namespace ui {
+
+enum class DomCode;
+
+class EVENTS_BASE_EXPORT PlatformKeyMap {

[chongz, 2016/02/12 16:04:03]

Currently other platforms have their own way of getting DomKey. But I have
discovered some issues, if it cannot be fixed I probably have to build the
KeyMap for them as well.

+ public:
+  // Create and load key map table with specified keyboard layout.
+  explicit PlatformKeyMap(HKL layout);
+
+  // Returns the DomKey 'meaning' of |code| in the context of specified
+  // |ui_event_flags| and stored keyboard layout.
+  DomKey DomCodeAndFlagsToDomKey(DomCode code,
+                                 int ui_event_flags /*EventFlags*/) const;

[Wez, 2016/02/12 21:29:38]

nit: No need for the EventFlags comment.

+
+  // Returns the DomKey 'meaning' of |code| in the context of specified
+  // |ui_event_flags| and the keyboard layout of current thread.
+  // Will load/update key map table when:
+  // 1. First call to this method.
+  // 2. Or keyboard layout of current thread was changed.

[Wez, 2016/02/12 21:29:38]

nit: Suggest replacing lines 3-5 with just:
" // Updates a per-thread key map cache whenever the layout changes."

which should be sufficient to get across that it's a non-trivial operation in
some cases.

nit: Related to this, should we provide an explicit function to trigger a layout
update, that we can call in response to WM_INPUTLANGCHANGE, for example, so as
to front-load the work ahead of any actual input?

+  static DomKey DomCodeAndFlagsToDomKeyStatic(
+      DomCode code,
+      int ui_event_flags /*EventFlags*/);

[Wez, 2016/02/12 21:29:37]

nit: No need for the EventFlags comment here, please - should be obvious from
the parameter name & context.

+
+ private:
+  PlatformKeyMap();
+
+  void UpdateLayout(HKL layout);
+
+  HKL keyboard_layout_ = 0;
+
+  typedef std::pair<DomCode, int /*EventFlags*/> DomCodeEventFlagsPair;
+  struct DomCodeEventFlagsPairHash {

[chongz, 2016/02/12 16:04:03]

Have to do this because we only have PairHash for int

[Wez, 2016/02/12 21:29:38]

So ugly! OK... how about using std::pair<int,int> as the typedef, with a comment
that we're treating DomCode as an int for simplicity?

+    size_t operator()(DomCodeEventFlagsPair code_flags) const {
+      return base::HashInts(static_cast<int>(code_flags.first),
+                            code_flags.second);
+    }
+  };
+  typedef std::unordered_map<DomCodeEventFlagsPair,
+                             DomKey,
+                             DomCodeEventFlagsPairHash>
+      DomCodeToKeyMap;
+  DomCodeToKeyMap code_key_map_;

[Wez, 2016/02/12 21:29:38]

nit: Suggest calling this code_to_key_map_ or just code_to_key_ (that it is a
map should be obvious from context and type name)

+
+  DISALLOW_COPY_AND_ASSIGN(PlatformKeyMap);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_KEYCODES_PLATFORM_KEY_MAP_WIN_H_