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 d3b19197b4b57628c162577e6925f8346705f154..3df2aae03d2cacfc73db4a02074d3e0ebbfb2625 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -655,6 +655,7 @@ 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.
@@ -770,6 +771,7 @@ 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);
@@ -858,6 +860,19 @@ void Shell::SetMonitorWorkAreaInsets(Window* contains,
                     OnMonitorWorkAreaInsetsChanged());
 }
 
+void Shell::OnLoginStateChange(bool logged_in, bool is_guest) {
+  FOR_EACH_OBSERVER(ShellObserver, observers_,
+                    OnLoginStateChange(logged_in, is_guest));
+}
+
+void Shell::OnExit() {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnExit());
+}
+
+void Shell::OnLockStateChange(bool locked) {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnLockStateChange(locked));
+}
+
 void Shell::CreateLauncher() {
   if (launcher_.get())
     return;