Return AltGraph for right-Alt keydown/keyup, under layouts which use AltGraph.

ui/events/keycodes/platform_key_map_win.cc

 // 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.
 
 #include "ui/events/keycodes/platform_key_map_win.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/lazy_instance.h"
@@ skipping 268 matching lines @@
 PlatformKeyMap::PlatformKeyMap() {}
 
 PlatformKeyMap::PlatformKeyMap(HKL layout) {
   UpdateLayout(layout);
 }
 
 PlatformKeyMap::~PlatformKeyMap() {}
 
 DomKey PlatformKeyMap::DomKeyFromKeyboardCodeImpl(KeyboardCode key_code,
                                                   int flags) const {
+  // Windows expresses right-Alt as VKEY_MENU with the extended flag set.
+  // This key should generate AltGraph under layouts which use that modifier.
+  if (key_code == VKEY_MENU && (flags & EF_IS_EXTENDED_KEY) && has_alt_graph_) {
+    return DomKey::ALT_GRAPH;
+  }
+
   DomKey key = NonPrintableKeyboardCodeToDomKey(key_code, keyboard_layout_);
   if (key != DomKey::NONE)
     return key;
 
   const int flags_to_try[] = {
       // Trying to match Firefox's behavior and UIEvents DomKey guidelines.
       // If the combination doesn't produce a printable character, the key value
       // should be the key with no modifiers except for Shift and AltGr.
       // See https://w3c.github.io/uievents/#keys-guidelines
       flags,
@@ skipping 40 matching lines @@
   if (layout == keyboard_layout_)
     return;
 
   BYTE keyboard_state_to_restore[256];
   if (!::GetKeyboardState(keyboard_state_to_restore))
     return;
 
   // TODO(chongz): Optimize layout switching (see crbug.com/587147).
   keyboard_layout_ = layout;
   printable_keycode_to_key_.clear();
+  has_alt_graph_ = false;
 
   // Map size for some sample keyboard layouts:
   // US: 476, French: 602, Persian: 482, Vietnamese: 1436
   printable_keycode_to_key_.reserve(1500);
 
   for (int modifier_combination = 0;
        modifier_combination <= kModifierFlagsCombinations;
        ++modifier_combination) {
     BYTE keyboard_state[256];
     memset(keyboard_state, 0, sizeof(keyboard_state));
@@ skipping 19 matching lines @@
                                                    flags)] =
               DomKey::DeadKeyFromCombiningCharacter(translated_chars[0]);
         } else {
           // TODO(chongz): Check if this will actually happen.
         }
       } else if (rv == 1) {
         if (translated_chars[0] >= 0x20) {
           printable_keycode_to_key_[std::make_pair(static_cast<int>(key_code),
                                                    flags)] =
               DomKey::FromCharacter(translated_chars[0]);
+
+          // Detect whether the layout makes use of AltGraph.
+          if (flags & EF_ALTGR_DOWN) {
+            has_alt_graph_ = true;
+          }
         } else {
           // Ignores legacy non-printable control characters.
         }
       } else {
         // TODO(chongz): Handle rv <= -2 and rv >= 2.
       }
     }
   }
   ::SetKeyboardState(keyboard_state_to_restore);
 }
 
 }  // namespace ui