[Mac] Produce correct DomKey when Ctrl/Shift/Command is down

ui/events/keycodes/keyboard_code_conversion_mac.mm

 // 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.
 
 #import "ui/events/keycodes/keyboard_code_conversion_mac.h"
 
 #include <algorithm>
 
 #import <Carbon/Carbon.h>
 
@@ skipping 728 matching lines @@
 DomCode DomCodeFromNSEvent(NSEvent* event) {
   return ui::KeycodeConverter::NativeKeycodeToDomCode([event keyCode]);
 }
 
 DomKey DomKeyFromNSEvent(NSEvent* event) {
   // Apply the lookup based on the character first since that has the
   // Keyboard layout and modifers already applied; whereas the keyCode
   // doesn't.
   if ([event type] == NSKeyDown || [event type] == NSKeyUp) {
     NSString* characters = [event characters];
-    if ([characters length] > 0)
-      return DomKeyFromCharCode([characters characterAtIndex:0]);
+    if ([characters length] > 0) {
+      unichar dom_key_char =
+          [characters characterAtIndex:[characters length] - 1];

[chongz, 2016/02/17 22:54:05]

Use last character because e.g. On French keyboard [+a will produce "^q", DomKey
should be 'q'.

+      if ([event modifierFlags] != 0 && std::iscntrl(dom_key_char)) {
+        // According to spec if the key combination produces a non-printable
+        // character, the key value should be the character without modifiers.
+        // See https://w3c.github.io/uievents/#keys-guidelines
+        NSString* unmodified_characters = [event charactersIgnoringModifiers];
+        if ([unmodified_characters length] > 0) {
+          unichar unmodified_char = [unmodified_characters
+              characterAtIndex:[unmodified_characters length] - 1];
+          dom_key_char = unmodified_char;
+        }
+      }
+      return DomKeyFromCharCode(dom_key_char);
+    }
   }
   return DomKeyFromKeyCode([event keyCode]);
 }
 
 }  // namespace ui