Release capture when locking screen

The capture window will not receive events while locked because
there is an extra mechanism to block events in locked state, but
having capture window in locked state will make lock UI unusable
by mouse/touch.

Explicitly release capture so that mouse/touch event works
when locked.

BUG=788782
TEST=covered by unittest

Change-Id: I01849f71ec0f059a21b433295fbdf816962d44d4
Reviewed-on: https://chromium-review.googlesource.com/1112938Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570100}

ash/login/ui/lock_screen.cc

@@ -26,6 +26,7 @@
 #include "ui/compositor/layer.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
+#include "ui/wm/core/capture_controller.h"
 
 namespace ash {
 namespace {
@@ -71,6 +72,9 @@ LockScreen* LockScreen::Get() {
 // static
 void LockScreen::Show(ScreenType type) {
   CHECK(!instance_);
+  // Capture should be released when locked.
+  ::wm::CaptureController::Get()->SetCapture(nullptr);
+
   instance_ = new LockScreen(type);
 
   instance_->window_ = new LockWindow();

ash/login/ui/lock_window_unittest.cc

@@ -9,6 +9,7 @@
 #include "ash/login/ui/login_big_user_view.h"
 #include "ash/login/ui/login_keyboard_test_base.h"
 #include "ash/login/ui/login_test_utils.h"
+#include "ui/wm/core/capture_controller.h"
 
 namespace ash {
 
@@ -31,4 +32,13 @@ TEST_F(LockWindowVirtualKeyboardTest, VirtualKeyboardDoesNotCoverAuthView) {
       auth_view->GetBoundsInScreen().Intersects(GetKeyboardBoundsInScreen()));
 }
 
+TEST_F(LockWindowVirtualKeyboardTest, ReleaseCapture) {
+  std::unique_ptr<aura::Window> window0(CreateTestWindowInShellWithId(0));
+  ::wm::CaptureController::Get()->SetCapture(window0.get());
+  ASSERT_EQ(window0.get(), ::wm::CaptureController::Get()->GetCaptureWindow());
+
+  ASSERT_NO_FATAL_FAILURE(ShowLockScreen());
+  EXPECT_FALSE(::wm::CaptureController::Get()->GetCaptureWindow());
+}
+
 }  // namespace ash