UMA data collection for docked windows

ash/wm/dock/docked_window_layout_manager.h

Index: ash/wm/dock/docked_window_layout_manager.h
diff --git a/ash/wm/dock/docked_window_layout_manager.h b/ash/wm/dock/docked_window_layout_manager.h
index f380f77d5afca0a0ec1b7fa1ccc1e417eb10661d..58d1efce3f2fe0f363acb6a6b522c62941c5fdb7 100644
--- a/ash/wm/dock/docked_window_layout_manager.h
+++ b/ash/wm/dock/docked_window_layout_manager.h
@@ -45,6 +45,21 @@ class DockedWindowResizerTest;
 class ShelfLayoutManager;
 class WorkspaceController;
 
+// User action recorded for use in UMA histograms.
+enum DockedAction {
+  DOCKED_ACTION_CANCEL,     // Dragged into or out of dock but cancelled.
+  DOCKED_ACTION_DOCK,       // Dragged and docked a window.
+  DOCKED_ACTION_UNDOCK,     // Dragged and undocked a window.
+  DOCKED_ACTION_RESIZE,     // Resized a docked window.
+  DOCKED_ACTION_REORDER,    // Reordered docked windows.
+  DOCKED_ACTION_EVICT,      // A docked window could not stay docked.
+  DOCKED_ACTION_MAXIMIZE,   // Maximized a docked window.
+  DOCKED_ACTION_MINIMIZE,   // Minimized a docked window.
+  DOCKED_ACTION_RESTORE,    // Restored a docked window that was minimized.
+  DOCKED_ACTION_CLOSE,      // Closed a window while it was docked.
+  DOCKED_ACTION_COUNT,      // Maximum value of this enum for histograms use.
+};
+
 struct WindowWithHeight {
   explicit WindowWithHeight(aura::Window* window) :
     window_(window),
@@ -267,6 +282,10 @@ class ASH_EXPORT DockedWindowLayoutManager
   // are currently focused.
   aura::Window* last_active_window_;
 
+  // Number of windows that were docked last time when a window was docked or
+  // undocked.
+  int previous_docked_windows_;
+
   // Widget used to paint a background for the docked area.
   scoped_ptr<views::Widget> background_widget_;