Converts overview to use common ash types

ash/metrics/user_metrics_recorder.h

Index: ash/metrics/user_metrics_recorder.h
diff --git a/ash/metrics/user_metrics_recorder.h b/ash/metrics/user_metrics_recorder.h
index f372920d1f0fdf15709b0b6587b31c82c6b96378..985a8f848af19eba5aa41d9e6c63c0d8790a831b 100644
--- a/ash/metrics/user_metrics_recorder.h
+++ b/ash/metrics/user_metrics_recorder.h
@@ -127,16 +127,6 @@ enum UserMetricsAction {
   UMA_WINDOW_MAXIMIZE_BUTTON_MAXIMIZE_LEFT,
   UMA_WINDOW_MAXIMIZE_BUTTON_MAXIMIZE_RIGHT,
 
-  // Thumbnail sized overview of windows triggered by pressing the overview key.
-  UMA_WINDOW_OVERVIEW,

[James Cook, 2016/05/27 00:02:50]

FYI, I asked kuscher@ if we need to maintain these metrics at all. Unfortunately
we do (apparently overview mode is being tweaked soon), but there may be other
classes of metrics we can just remove. I'll follow up with him.

-
-  // User selected a window in overview mode different from the
-  // previously-active window.
-  UMA_WINDOW_OVERVIEW_ACTIVE_WINDOW_CHANGED,
-
-  // Selecting a window in overview mode by pressing the enter key.
-  UMA_WINDOW_OVERVIEW_ENTER_KEY,
-
   // Window selection started by beginning an alt+tab cycle. This does not count
   // each step through an alt+tab cycle.
   UMA_WINDOW_CYCLE,