Cancel partial screenshot UI when lock happens.

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 3b0b0b8b3664673c117cede8f80b73b0e709c717..8f4b07281205d13a722bda3c3beddbec6bd6c132 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -657,6 +657,7 @@ void Shell::Init() {
   DCHECK_EQ(1U, GetRootWindowEventFilterCount());
   partial_screenshot_filter_.reset(new internal::PartialScreenshotEventFilter);
   AddRootWindowEventFilter(partial_screenshot_filter_.get());
+  AddShellObserver(partial_screenshot_filter_.get());
 
   // Then AcceleratorFilter and InputMethodEventFilter must be added (in this
   // order) since they have the second highest priority.
@@ -772,6 +773,7 @@ void Shell::Init() {
 
   drag_drop_controller_.reset(new internal::DragDropController);
   power_button_controller_.reset(new PowerButtonController);
+  AddShellObserver(power_button_controller_.get());
   video_detector_.reset(new VideoDetector);
   window_cycle_controller_.reset(new WindowCycleController);
   monitor_controller_.reset(new internal::MonitorController);
@@ -860,6 +862,18 @@ void Shell::SetMonitorWorkAreaInsets(Window* contains,
                     OnMonitorWorkAreaInsetsChanged());
 }
 
+void Shell::OnLoginStateChanged(user::LoginStatus status) {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnLoginStateChanged(status));
+}
+
+void Shell::OnAppTerminating() {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnAppTerminating());
+}
+
+void Shell::OnLockStateChanged(bool locked) {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnLockStateChanged(locked));
+}
+
 void Shell::CreateLauncher() {
   if (launcher_.get())
     return;