Fix alt-tab on fullscreen task manager

Currently for fullscreen window, Ash lets the browser or apps to process
the accelerator first. However, focus_manager handles "alt-tab" as a
"Tab" traversal key event. This cl fixes this bug.

Bug: 832739
Test: New test FocusManagerTest.IsTabTraversalKeyEvent
Change-Id: I6252a5614390223c581d032d39dbad1c84de6b48
Reviewed-on: https://chromium-review.googlesource.com/1014651
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551377}

ui/views/focus/focus_manager.cc

@@ -485,7 +485,8 @@ bool FocusManager::HasPriorityHandler(
 
 // static
 bool FocusManager::IsTabTraversalKeyEvent(const ui::KeyEvent& key_event) {
-  return key_event.key_code() == ui::VKEY_TAB && !key_event.IsControlDown();
+  return key_event.key_code() == ui::VKEY_TAB &&
+         (!key_event.IsControlDown() && !key_event.IsAltDown());
 }
 
 void FocusManager::ViewRemoved(View* removed) {

ui/views/focus/focus_manager_unittest.cc

@@ -913,4 +913,19 @@ TEST_F(FocusManagerTest, AdvanceFocusStaysInWidget) {
   EXPECT_EQ(widget_view, GetFocusManager()->GetFocusedView());
 }
 
+// Verifies if a key event is a tab traversal key event or not.
+TEST_F(FocusManagerTest, IsTabTraversalKeyEvent) {
+  ui::KeyEvent event(ui::ET_KEY_PRESSED, ui::VKEY_TAB, ui::EF_NONE);
+  EXPECT_TRUE(FocusManager::IsTabTraversalKeyEvent(event));
+
+  event = ui::KeyEvent(ui::ET_KEY_PRESSED, ui::VKEY_TAB, ui::EF_SHIFT_DOWN);
+  EXPECT_TRUE(FocusManager::IsTabTraversalKeyEvent(event));
+
+  event = ui::KeyEvent(ui::ET_KEY_PRESSED, ui::VKEY_TAB, ui::EF_CONTROL_DOWN);
+  EXPECT_FALSE(FocusManager::IsTabTraversalKeyEvent(event));
+
+  event = ui::KeyEvent(ui::ET_KEY_PRESSED, ui::VKEY_TAB, ui::EF_ALT_DOWN);
+  EXPECT_FALSE(FocusManager::IsTabTraversalKeyEvent(event));
+}
+
 }  // namespace views