Fix crash in keyboard_unittests.

Test: keyboard_unittests
Change-Id: If0144253d227b3d46813fa2e7f339359fd70874c
Reviewed-on: https://chromium-review.googlesource.com/1109602Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569173}

ui/keyboard/keyboard_controller_unittest.cc

@@ -799,6 +799,9 @@ TEST_F(KeyboardControllerAnimationTest, FloatingKeyboardEnsureCaretInWorkArea) {
   RunAnimationForLayer(layer);
 
   EXPECT_TRUE(keyboard_window()->IsVisible());
+
+  // Unfocus from the MockTextInputClient before destroying it.
+  ui()->GetInputMethod()->DetachTextInputClient(&mock_input_client);
 }
 
 // Checks DisableKeyboard() doesn't clear the observer list.