Allows to fire VKEY_UNKNOWN key events.

On Linux, we have keys with keycode=VKEY_UNKNOWN, for example, ISO_LEVEL3_LATCH key.  We have to emit keydown/up events appropriately even if keycode=VKEY_UNKNOWN.

Just FYI: Firefox also fires keyevents with keycode=0, so the behavior will be compatible.  Compared to IE and Chrome on Windows, it's still compatible because there is no such key as ISO_LEVEL3_LATCH, etc. on Windows.

BUG=402320
TEST=Done manually.

Review URL: https://codereview.chromium.org/665863002

Cr-Commit-Position: refs/heads/master@{#300438}

ui/aura/window_event_dispatcher_unittest.cc

@@ -342,14 +342,14 @@ TEST_F(WindowEventDispatcherTest, CanProcessEventsWithinSubtree) {
   w3->parent()->RemoveChild(w3.get());
 }
 
-TEST_F(WindowEventDispatcherTest, IgnoreUnknownKeys) {
+TEST_F(WindowEventDispatcherTest, DontIgnoreUnknownKeys) {
   ConsumeKeyHandler handler;
   root_window()->AddPreTargetHandler(&handler);
 
   ui::KeyEvent unknown_event(ui::ET_KEY_PRESSED, ui::VKEY_UNKNOWN, ui::EF_NONE);
   DispatchEventUsingWindowDispatcher(&unknown_event);
-  EXPECT_FALSE(unknown_event.handled());
-  EXPECT_EQ(0, handler.num_key_events());
+  EXPECT_TRUE(unknown_event.handled());
+  EXPECT_EQ(1, handler.num_key_events());
 
   handler.Reset();
   ui::KeyEvent known_event(ui::ET_KEY_PRESSED, ui::VKEY_A, ui::EF_NONE);

ui/aura/window_targeter.cc

@@ -104,10 +104,6 @@ ui::EventTarget* WindowTargeter::FindTargetForLocatedEvent(
 Window* WindowTargeter::FindTargetForKeyEvent(Window* window,
                                               const ui::KeyEvent& key) {
   Window* root_window = window->GetRootWindow();
-  if (key.key_code() == ui::VKEY_UNKNOWN &&
-      (key.flags() & ui::EF_IME_FABRICATED_KEY) == 0 &&
-      key.GetCharacter() == 0)
-    return NULL;
   client::FocusClient* focus_client = client::GetFocusClient(root_window);
   Window* focused_window = focus_client->GetFocusedWindow();
   if (!focused_window)