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

ui/events/keycodes/platform_key_map_win.cc

Index: ui/events/keycodes/platform_key_map_win.cc
diff --git a/ui/events/keycodes/platform_key_map_win.cc b/ui/events/keycodes/platform_key_map_win.cc
index 439384c634941d9eb9017b047e3dd464860a9f9f..c5a290c4dd8adf3bad92e0694768a7fb35dd660d 100644
--- a/ui/events/keycodes/platform_key_map_win.cc
+++ b/ui/events/keycodes/platform_key_map_win.cc
@@ -287,6 +287,9 @@ PlatformKeyMap::~PlatformKeyMap() {}
 DomKey PlatformKeyMap::DomKeyFromKeyboardCodeImpl(KeyboardCode key_code,
                                                   int flags) const {
   DomKey key = NonPrintableKeyboardCodeToDomKey(key_code, keyboard_layout_);
+  if (key == DomKey::ALT && (flags & EF_IS_EXTENDED_KEY) && has_alt_graph_) {

[garykac, 2017/01/18 15:55:29]

Could you add a brief comment above this line?

[Wez, 2017/01/18 21:36:35]

Done.

+    return DomKey::ALT_GRAPH;
+  }
   if (key != DomKey::NONE)
     return key;
 
@@ -346,6 +349,7 @@ void PlatformKeyMap::UpdateLayout(HKL layout) {
   // 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
@@ -385,6 +389,11 @@ void PlatformKeyMap::UpdateLayout(HKL layout) {
           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.
         }