Fixes accelerator shortcut text for unknown keys

For unknown key codes presenting in an accelerator 0 is added
to the shortcut text. This results in unprintable character to be used
on extensions shortcuts settings page.

Bug: 936812
Change-Id: I5301660d8110defd908146862a230666af09a07d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1497072
Commit-Queue: Alexander Yashkin <a-v-y@yandex-team.ru>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638507}

ui/base/accelerators/accelerator.cc

@@ -161,7 +161,10 @@ base::string16 Accelerator::GetShortcutText() const {
       key = static_cast<wchar_t>(key_code_);
     else
       key = LOWORD(::MapVirtualKeyW(key_code_, MAPVK_VK_TO_CHAR));
-    shortcut += key;
+    // If there is no translation for the given |key_code_| (e.g.
+    // VKEY_UNKNOWN), |::MapVirtualKeyW| returns 0.
+    if (key != 0)
+      shortcut += key;
 #elif defined(USE_AURA) || defined(OS_MACOSX) || defined(OS_ANDROID)
     const uint16_t c = DomCodeToUsLayoutCharacter(
         UsLayoutKeyboardCodeToDomCode(key_code_), false);

ui/base/accelerators/accelerator_unittest.cc

@@ -62,4 +62,9 @@ TEST(AcceleratorTest, GetShortcutText) {
   }
 }
 
+TEST(AcceleratorTest, ShortcutTextForUnknownKey) {
+  const Accelerator accelerator(VKEY_UNKNOWN, EF_NONE);
+  EXPECT_EQ(base::string16(), accelerator.GetShortcutText());
+}
+
 }  // namespace ui