Make ToplevelWindowEventFilter and WorkspaceEventFilter into event handlers.

ash/wm/workspace/workspace2.h

Index: ash/wm/workspace/workspace2.h
===================================================================
--- ash/wm/workspace/workspace2.h	(revision 155914)
+++ ash/wm/workspace/workspace2.h	(working copy)
@@ -21,7 +21,7 @@
 namespace ash {
 namespace internal {
 
-class WorkspaceEventFilter;
+class WorkspaceEventHandler;
 class WorkspaceManager2;
 
 // Workspace is used to maintain either a single maximized windows (including
@@ -61,7 +61,7 @@
   aura::Window* window_;
 
   // Owned by |window_|.
-  WorkspaceEventFilter* event_filter_;
+  WorkspaceEventHandler* event_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(Workspace2);
 };