Converts MruWindowTracker to work with common types

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index fd582f5bb6a81c7afeaf0b620d2e255a9dfd8100..659251c86cceab96f86a97a1906ce47cf8dd806f 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -72,6 +72,11 @@ class ASH_EXPORT WmShell {
   virtual bool IsUserSessionBlocked() = 0;
   virtual bool IsScreenLocked() = 0;
 
+  // Returns true if |window| can be shown for the current user. This is
+  // intended to check if the current users matches the user associated with

[James Cook, 2016/06/07 01:21:04]

nit: "current users" -> "current user" (unless this is somehow dealing with
multiprofile/multiuser, which I'm guessing not).

[sky, 2016/06/07 02:46:21]

Done.

+  // |window|.
+  virtual bool CanShowWindowForUser(WmWindow* window) = 0;
+
   // See aura::client::CursorClient for details on these.
   virtual void LockCursor() = 0;
   virtual void UnlockCursor() = 0;